Textbook: Reactions and Equations | Technical Science for Grade 10 PDF Download

 Page 1


 technical science GRADE 10 247
chapter 10 reactions and equations
In Chapter 8 you learned about the properties of materials, and in Chapter 9 you learned 
about the particles and substances that make up those materials. In Chapter 10 you learn 
how the atoms join with each other in exact ratios. Look at the map below to see where the 
chapters are going.
…but here we 
answer them!
In chapter 8 we study 
materials on the macro-
scale. We study, for 
example, strength, density, 
magnetic properties, 
melting and boiling.
In chapter 9 we study 
materials on the nano-
scale; that is, the atoms 
and molecules that 
make up the materials 
and use the PKMM.
chapter 10 uses the 
PKMM to understand how 
elements and compounds 
react and how ions form.
chapter 8 leaves some 
questions unanswered about 
the properties of materials… 
what are the reasons why these 
materials have these properties?
In chapter 11 we use the PKMM to answer 
the questions about:
 ? why some materials are magnetic
 ? how they conduct heat and electricity
 ? why boiling points depend on altitude
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   247 2015/12/17   10:03 AM
Page 2


 technical science GRADE 10 247
chapter 10 reactions and equations
In Chapter 8 you learned about the properties of materials, and in Chapter 9 you learned 
about the particles and substances that make up those materials. In Chapter 10 you learn 
how the atoms join with each other in exact ratios. Look at the map below to see where the 
chapters are going.
…but here we 
answer them!
In chapter 8 we study 
materials on the macro-
scale. We study, for 
example, strength, density, 
magnetic properties, 
melting and boiling.
In chapter 9 we study 
materials on the nano-
scale; that is, the atoms 
and molecules that 
make up the materials 
and use the PKMM.
chapter 10 uses the 
PKMM to understand how 
elements and compounds 
react and how ions form.
chapter 8 leaves some 
questions unanswered about 
the properties of materials… 
what are the reasons why these 
materials have these properties?
In chapter 11 we use the PKMM to answer 
the questions about:
 ? why some materials are magnetic
 ? how they conduct heat and electricity
 ? why boiling points depend on altitude
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   247 2015/12/17   10:03 AM
248 c hapter 10 REACTIONS AND EqUATIONS
unit 10.1 compounds can decompose to elements 
In Chapter 9 you learned how people, long ago, 
obtained elements from special kinds of rock. The rock 
contained compounds, and the compounds broke down 
into elements.
In 1774, Joseph Priestley in England was investigating 
an orange powder called “calx of mercury”. The powder 
was in a small dish, floating on mercury in a narrow 
tube. You see the apparatus in Figure 10.1. He used two 
big magnifying glasses to focus the energy from the Sun 
onto the powder. 
The Sun heated the orange powder inside the glass tube. 
It turned a dark colour and it gave off a gas. Priestly did 
not know what this gas was, but he used larger apparatus 
to collect enough of the gas to breathe some himself. He 
wrote in his notebook that it made him feel very good.
Nobody knew what the gas was and it did not yet have 
a name. But Priestley’s discovery became a key idea in 
understanding chemistry. You can find the story in the 
Resource Pages.
activity 1 r ead about Joseph Priestley’s discovery
Find the story about Joseph Priestley in the Resource Pages. Read it and answer the questions 
below in your notebook. 
Questions
1. What was the gas that Priestley discovered? Write two paragraphs to describe Priestley’s 
experiment.
2. After he heated the orange powder, the mercury liquid in the tube was pushed down. 
Why did the liquid get pushed down?
3. He wrote in his notebook that breathing the gas made him feel good and the mice seemed 
to like it also. Why did the gas have that effect?
4. He also put a burning candle in a jar full of the gas. What happened to the candle flame?
Joseph Priestley had actually discovered oxygen. He was able to show that oxygen is one of the 
gases in air, and that all animals and humans need oxygen to live. He also showed that plants 
produce oxygen, and so plants replace the oxygen that humans, animals and fires remove from 
the atmosphere. 
Figure 10.1 Joseph Priestley found that the 
heat of the Sun made the orange substance 
give off a gas.
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   248 2015/12/17   10:03 AM
Page 3


 technical science GRADE 10 247
chapter 10 reactions and equations
In Chapter 8 you learned about the properties of materials, and in Chapter 9 you learned 
about the particles and substances that make up those materials. In Chapter 10 you learn 
how the atoms join with each other in exact ratios. Look at the map below to see where the 
chapters are going.
…but here we 
answer them!
In chapter 8 we study 
materials on the macro-
scale. We study, for 
example, strength, density, 
magnetic properties, 
melting and boiling.
In chapter 9 we study 
materials on the nano-
scale; that is, the atoms 
and molecules that 
make up the materials 
and use the PKMM.
chapter 10 uses the 
PKMM to understand how 
elements and compounds 
react and how ions form.
chapter 8 leaves some 
questions unanswered about 
the properties of materials… 
what are the reasons why these 
materials have these properties?
In chapter 11 we use the PKMM to answer 
the questions about:
 ? why some materials are magnetic
 ? how they conduct heat and electricity
 ? why boiling points depend on altitude
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   247 2015/12/17   10:03 AM
248 c hapter 10 REACTIONS AND EqUATIONS
unit 10.1 compounds can decompose to elements 
In Chapter 9 you learned how people, long ago, 
obtained elements from special kinds of rock. The rock 
contained compounds, and the compounds broke down 
into elements.
In 1774, Joseph Priestley in England was investigating 
an orange powder called “calx of mercury”. The powder 
was in a small dish, floating on mercury in a narrow 
tube. You see the apparatus in Figure 10.1. He used two 
big magnifying glasses to focus the energy from the Sun 
onto the powder. 
The Sun heated the orange powder inside the glass tube. 
It turned a dark colour and it gave off a gas. Priestly did 
not know what this gas was, but he used larger apparatus 
to collect enough of the gas to breathe some himself. He 
wrote in his notebook that it made him feel very good.
Nobody knew what the gas was and it did not yet have 
a name. But Priestley’s discovery became a key idea in 
understanding chemistry. You can find the story in the 
Resource Pages.
activity 1 r ead about Joseph Priestley’s discovery
Find the story about Joseph Priestley in the Resource Pages. Read it and answer the questions 
below in your notebook. 
Questions
1. What was the gas that Priestley discovered? Write two paragraphs to describe Priestley’s 
experiment.
2. After he heated the orange powder, the mercury liquid in the tube was pushed down. 
Why did the liquid get pushed down?
3. He wrote in his notebook that breathing the gas made him feel good and the mice seemed 
to like it also. Why did the gas have that effect?
4. He also put a burning candle in a jar full of the gas. What happened to the candle flame?
Joseph Priestley had actually discovered oxygen. He was able to show that oxygen is one of the 
gases in air, and that all animals and humans need oxygen to live. He also showed that plants 
produce oxygen, and so plants replace the oxygen that humans, animals and fires remove from 
the atmosphere. 
Figure 10.1 Joseph Priestley found that the 
heat of the Sun made the orange substance 
give off a gas.
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   248 2015/12/17   10:03 AM
 technical science GRADE 10 249
Mercury is an element and so is oxygen. Priestley had broken the compound mercuric oxide 
down into its two elements! In the periodic table you can find the elements oxygen (
8
O) and 
mercury (
80
Hg).
The orange compound, mercuric oxide (HgO), is a powder. Each grain of the powder is made 
up of billions of mercury atoms joined to billions of oxygen atoms in a regular pattern. This 
structure is called a lattice.
The energy from the sun, which came through Priestley’s burning-glasses in Figure 10.1, gave 
the atoms enough energy to break apart. The atoms of oxygen formed oxygen molecules. The 
mercury atoms joined together in giant molecules that grew so big that he could see them as 
little drops of mercury.
When atoms that were joined together break apart, and join with other atoms, we say that a 
reaction has happened.
Chemists have ways to summarise changes like this. Let’s begin with a statement in words: 
Mercuric oxide breaks up to form mercury and oxygen. 
Then we do a drawing to show what happened. We call this a picture model. 
Figure 10.2 The giant molecule of mercuric oxide broke up to form ten mercury atoms and five oxygen molecules. 
The arrow tells us that the change was from mercuric oxide to mercury and oxygen.
A mercuric oxide
giant molecule
with
energy
from
the sun
One atom of mercury joining
with other mercury atoms
Two oxygen atoms forming
an oxygen molecule
We can count 10 mercury atoms in the mercuric oxide giant molecule on the left of the arrow; 
there must be the same number of mercury atoms on the right. We count 10 oxygen atoms 
(coloured red) in the mercuric oxide on the left, and there must be the same number of oxygen 
atoms on the right. Oxygen atoms join together in pairs that we call O
2
 molecules, but there are 
still 10 oxygen atoms.
In a chemical reaction, matter is conserved. That means no atoms are destroyed and no new 
atoms are created. That is why we can talk about a chemical equation: the number of each kind 
of atom is equal on the left and the right sides.
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   249 2015/12/17   10:03 AM
Page 4


 technical science GRADE 10 247
chapter 10 reactions and equations
In Chapter 8 you learned about the properties of materials, and in Chapter 9 you learned 
about the particles and substances that make up those materials. In Chapter 10 you learn 
how the atoms join with each other in exact ratios. Look at the map below to see where the 
chapters are going.
…but here we 
answer them!
In chapter 8 we study 
materials on the macro-
scale. We study, for 
example, strength, density, 
magnetic properties, 
melting and boiling.
In chapter 9 we study 
materials on the nano-
scale; that is, the atoms 
and molecules that 
make up the materials 
and use the PKMM.
chapter 10 uses the 
PKMM to understand how 
elements and compounds 
react and how ions form.
chapter 8 leaves some 
questions unanswered about 
the properties of materials… 
what are the reasons why these 
materials have these properties?
In chapter 11 we use the PKMM to answer 
the questions about:
 ? why some materials are magnetic
 ? how they conduct heat and electricity
 ? why boiling points depend on altitude
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   247 2015/12/17   10:03 AM
248 c hapter 10 REACTIONS AND EqUATIONS
unit 10.1 compounds can decompose to elements 
In Chapter 9 you learned how people, long ago, 
obtained elements from special kinds of rock. The rock 
contained compounds, and the compounds broke down 
into elements.
In 1774, Joseph Priestley in England was investigating 
an orange powder called “calx of mercury”. The powder 
was in a small dish, floating on mercury in a narrow 
tube. You see the apparatus in Figure 10.1. He used two 
big magnifying glasses to focus the energy from the Sun 
onto the powder. 
The Sun heated the orange powder inside the glass tube. 
It turned a dark colour and it gave off a gas. Priestly did 
not know what this gas was, but he used larger apparatus 
to collect enough of the gas to breathe some himself. He 
wrote in his notebook that it made him feel very good.
Nobody knew what the gas was and it did not yet have 
a name. But Priestley’s discovery became a key idea in 
understanding chemistry. You can find the story in the 
Resource Pages.
activity 1 r ead about Joseph Priestley’s discovery
Find the story about Joseph Priestley in the Resource Pages. Read it and answer the questions 
below in your notebook. 
Questions
1. What was the gas that Priestley discovered? Write two paragraphs to describe Priestley’s 
experiment.
2. After he heated the orange powder, the mercury liquid in the tube was pushed down. 
Why did the liquid get pushed down?
3. He wrote in his notebook that breathing the gas made him feel good and the mice seemed 
to like it also. Why did the gas have that effect?
4. He also put a burning candle in a jar full of the gas. What happened to the candle flame?
Joseph Priestley had actually discovered oxygen. He was able to show that oxygen is one of the 
gases in air, and that all animals and humans need oxygen to live. He also showed that plants 
produce oxygen, and so plants replace the oxygen that humans, animals and fires remove from 
the atmosphere. 
Figure 10.1 Joseph Priestley found that the 
heat of the Sun made the orange substance 
give off a gas.
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   248 2015/12/17   10:03 AM
 technical science GRADE 10 249
Mercury is an element and so is oxygen. Priestley had broken the compound mercuric oxide 
down into its two elements! In the periodic table you can find the elements oxygen (
8
O) and 
mercury (
80
Hg).
The orange compound, mercuric oxide (HgO), is a powder. Each grain of the powder is made 
up of billions of mercury atoms joined to billions of oxygen atoms in a regular pattern. This 
structure is called a lattice.
The energy from the sun, which came through Priestley’s burning-glasses in Figure 10.1, gave 
the atoms enough energy to break apart. The atoms of oxygen formed oxygen molecules. The 
mercury atoms joined together in giant molecules that grew so big that he could see them as 
little drops of mercury.
When atoms that were joined together break apart, and join with other atoms, we say that a 
reaction has happened.
Chemists have ways to summarise changes like this. Let’s begin with a statement in words: 
Mercuric oxide breaks up to form mercury and oxygen. 
Then we do a drawing to show what happened. We call this a picture model. 
Figure 10.2 The giant molecule of mercuric oxide broke up to form ten mercury atoms and five oxygen molecules. 
The arrow tells us that the change was from mercuric oxide to mercury and oxygen.
A mercuric oxide
giant molecule
with
energy
from
the sun
One atom of mercury joining
with other mercury atoms
Two oxygen atoms forming
an oxygen molecule
We can count 10 mercury atoms in the mercuric oxide giant molecule on the left of the arrow; 
there must be the same number of mercury atoms on the right. We count 10 oxygen atoms 
(coloured red) in the mercuric oxide on the left, and there must be the same number of oxygen 
atoms on the right. Oxygen atoms join together in pairs that we call O
2
 molecules, but there are 
still 10 oxygen atoms.
In a chemical reaction, matter is conserved. That means no atoms are destroyed and no new 
atoms are created. That is why we can talk about a chemical equation: the number of each kind 
of atom is equal on the left and the right sides.
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   249 2015/12/17   10:03 AM
250 c hapter 10 REACTIONS AND EqUATIONS
Balancing a chemical equation
Hg is the symbol for mercury, and O is the symbol for oxygen. So we can write an equation, 
counting up the atoms on each side of the arrow:
 10 HgO 
?
 10 Hg + 5 O
2
In symbols, we are saying the same as the picture model in Figure 10.2 on the previous page.
If we wrote:
 14 HgO 
?
 14 Hg + 7 O
2
the ratio of HgO molecules to O
2
 molecules will remain the same, at two HgO to one O
2 
molecule.
Figure 10.3 Count the atoms on the left side and the right side of the arrow.
A mercuric oxide giant molecule
energy 
Mercury atoms Oxygen atoms 
Now the simplest way we can write the ratio is to write: 
 2HgO 
?
 2 Hg + O
2
This equation tells us that for every two HgO molecules, we get two Hg atoms and  
one O
2
 molecule. 
The equation is balanced because the number of Hg atoms is the same before and after the 
reaction, and the number of O atoms is also the same, before and after.
We have been looking at Joseph Priestley’s experiment that broke down mercuric oxide into 
elements; now let’s look at another famous experiment that broke down water. 
how scientists proved that water is a compound 
The alchemists long ago believed that water was an element. But scientists after Priestley 
suspected that water was not an element. 
In 1799, Alessandro Volta invented a kind of battery and wrote about it. Two scientists in 
England read what Volta wrote, and made a similar battery. They began experimenting with it 
immediately, to see whether they could break water into its elements. 
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   250 2015/12/17   10:03 AM
Page 5


 technical science GRADE 10 247
chapter 10 reactions and equations
In Chapter 8 you learned about the properties of materials, and in Chapter 9 you learned 
about the particles and substances that make up those materials. In Chapter 10 you learn 
how the atoms join with each other in exact ratios. Look at the map below to see where the 
chapters are going.
…but here we 
answer them!
In chapter 8 we study 
materials on the macro-
scale. We study, for 
example, strength, density, 
magnetic properties, 
melting and boiling.
In chapter 9 we study 
materials on the nano-
scale; that is, the atoms 
and molecules that 
make up the materials 
and use the PKMM.
chapter 10 uses the 
PKMM to understand how 
elements and compounds 
react and how ions form.
chapter 8 leaves some 
questions unanswered about 
the properties of materials… 
what are the reasons why these 
materials have these properties?
In chapter 11 we use the PKMM to answer 
the questions about:
 ? why some materials are magnetic
 ? how they conduct heat and electricity
 ? why boiling points depend on altitude
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   247 2015/12/17   10:03 AM
248 c hapter 10 REACTIONS AND EqUATIONS
unit 10.1 compounds can decompose to elements 
In Chapter 9 you learned how people, long ago, 
obtained elements from special kinds of rock. The rock 
contained compounds, and the compounds broke down 
into elements.
In 1774, Joseph Priestley in England was investigating 
an orange powder called “calx of mercury”. The powder 
was in a small dish, floating on mercury in a narrow 
tube. You see the apparatus in Figure 10.1. He used two 
big magnifying glasses to focus the energy from the Sun 
onto the powder. 
The Sun heated the orange powder inside the glass tube. 
It turned a dark colour and it gave off a gas. Priestly did 
not know what this gas was, but he used larger apparatus 
to collect enough of the gas to breathe some himself. He 
wrote in his notebook that it made him feel very good.
Nobody knew what the gas was and it did not yet have 
a name. But Priestley’s discovery became a key idea in 
understanding chemistry. You can find the story in the 
Resource Pages.
activity 1 r ead about Joseph Priestley’s discovery
Find the story about Joseph Priestley in the Resource Pages. Read it and answer the questions 
below in your notebook. 
Questions
1. What was the gas that Priestley discovered? Write two paragraphs to describe Priestley’s 
experiment.
2. After he heated the orange powder, the mercury liquid in the tube was pushed down. 
Why did the liquid get pushed down?
3. He wrote in his notebook that breathing the gas made him feel good and the mice seemed 
to like it also. Why did the gas have that effect?
4. He also put a burning candle in a jar full of the gas. What happened to the candle flame?
Joseph Priestley had actually discovered oxygen. He was able to show that oxygen is one of the 
gases in air, and that all animals and humans need oxygen to live. He also showed that plants 
produce oxygen, and so plants replace the oxygen that humans, animals and fires remove from 
the atmosphere. 
Figure 10.1 Joseph Priestley found that the 
heat of the Sun made the orange substance 
give off a gas.
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   248 2015/12/17   10:03 AM
 technical science GRADE 10 249
Mercury is an element and so is oxygen. Priestley had broken the compound mercuric oxide 
down into its two elements! In the periodic table you can find the elements oxygen (
8
O) and 
mercury (
80
Hg).
The orange compound, mercuric oxide (HgO), is a powder. Each grain of the powder is made 
up of billions of mercury atoms joined to billions of oxygen atoms in a regular pattern. This 
structure is called a lattice.
The energy from the sun, which came through Priestley’s burning-glasses in Figure 10.1, gave 
the atoms enough energy to break apart. The atoms of oxygen formed oxygen molecules. The 
mercury atoms joined together in giant molecules that grew so big that he could see them as 
little drops of mercury.
When atoms that were joined together break apart, and join with other atoms, we say that a 
reaction has happened.
Chemists have ways to summarise changes like this. Let’s begin with a statement in words: 
Mercuric oxide breaks up to form mercury and oxygen. 
Then we do a drawing to show what happened. We call this a picture model. 
Figure 10.2 The giant molecule of mercuric oxide broke up to form ten mercury atoms and five oxygen molecules. 
The arrow tells us that the change was from mercuric oxide to mercury and oxygen.
A mercuric oxide
giant molecule
with
energy
from
the sun
One atom of mercury joining
with other mercury atoms
Two oxygen atoms forming
an oxygen molecule
We can count 10 mercury atoms in the mercuric oxide giant molecule on the left of the arrow; 
there must be the same number of mercury atoms on the right. We count 10 oxygen atoms 
(coloured red) in the mercuric oxide on the left, and there must be the same number of oxygen 
atoms on the right. Oxygen atoms join together in pairs that we call O
2
 molecules, but there are 
still 10 oxygen atoms.
In a chemical reaction, matter is conserved. That means no atoms are destroyed and no new 
atoms are created. That is why we can talk about a chemical equation: the number of each kind 
of atom is equal on the left and the right sides.
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   249 2015/12/17   10:03 AM
250 c hapter 10 REACTIONS AND EqUATIONS
Balancing a chemical equation
Hg is the symbol for mercury, and O is the symbol for oxygen. So we can write an equation, 
counting up the atoms on each side of the arrow:
 10 HgO 
?
 10 Hg + 5 O
2
In symbols, we are saying the same as the picture model in Figure 10.2 on the previous page.
If we wrote:
 14 HgO 
?
 14 Hg + 7 O
2
the ratio of HgO molecules to O
2
 molecules will remain the same, at two HgO to one O
2 
molecule.
Figure 10.3 Count the atoms on the left side and the right side of the arrow.
A mercuric oxide giant molecule
energy 
Mercury atoms Oxygen atoms 
Now the simplest way we can write the ratio is to write: 
 2HgO 
?
 2 Hg + O
2
This equation tells us that for every two HgO molecules, we get two Hg atoms and  
one O
2
 molecule. 
The equation is balanced because the number of Hg atoms is the same before and after the 
reaction, and the number of O atoms is also the same, before and after.
We have been looking at Joseph Priestley’s experiment that broke down mercuric oxide into 
elements; now let’s look at another famous experiment that broke down water. 
how scientists proved that water is a compound 
The alchemists long ago believed that water was an element. But scientists after Priestley 
suspected that water was not an element. 
In 1799, Alessandro Volta invented a kind of battery and wrote about it. Two scientists in 
England read what Volta wrote, and made a similar battery. They began experimenting with it 
immediately, to see whether they could break water into its elements. 
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   250 2015/12/17   10:03 AM
 technical science GRADE 10 251
You could actually do this yourself, using the apparatus 
you see in Figure 10.4.
You see a 9 volt battery connected to 2 stainless steel 
electrodes. Each electrode is inside a clear plastic tube, closed 
at the top but open at the bottom.
Each electrode is in contact with the water. When you 
connect the battery, bubbles begin to form at each electrode 
and fi ll the plastic tubes with gas. 
But you get twice the volume of gas at the negative electrode 
compared to the positive electrode. When you test the gases, 
you fi nd that the gas that collected at the negative electrode 
is hydrogen, and the gas at the positive electrode is oxygen. 
So water is not an element – it is made of two elements, 
oxygen and hydrogen. Like the scientists in 1800, we make 
an inference* – we infer that there were twice as many 
hydrogen molecules as oxygen molecules. If we collected 
two billion hydrogen molecules, then we collected one 
billion oxygen molecules. 
In words, the reaction is:
water (by energy from the battery) breaks down into 
hydrogen and oxygen
We can model this with beads, or we can draw this: 
Figure 10.5 A picture model of water decomposing into hydrogen and oxygen
O
O O
O
O
O
O
O
O
O
H
H
H
H
H
H
H
H
H H
H
H
H
H
H
H
H
H
H
H
O
H H
O
H H
O
H H
O
H H
O
H H
O
H H
O
H H
O
H H
O
H H
O
H H
energy
from the
battery
The picture model must show a balanced equation. Count the number of oxygen atoms and 
hydrogen atoms on each side of the arrow. Are they equal?
In symbols, we can summarise that picture with this equation: 
 2H
2
O 
?
 2H
2
 + O
2
Think: What is the ratio of hydrogen atoms to oxygen atoms in water? Is the hydrogen:oxygen 
ratio 2:1 or 1:1 or 1:2?
Figure 10.4 The apparatus you need 
for decomposing water into its elements
prestik
9 V
plastic straws
small beaker with water
? ? inference – a conclusion you 
make after thinking about the 
observation
TechSci_G10-LB-Eng-DBE3_9781431522842.indb   251 2015/12/17   10:03 AM