Olympiad Test: Changes Around Us -2 - Class 6

To solve this problem, we need to understand the concept of conservation of mass. According to this principle, the mass of a substance remains constant during physical or chemical changes.
In this case, we are given that 10 gm of solid wax is melted. We need to determine the mass of the molten wax formed.
Key Point:
- The mass of the molten wax formed will be equal to the mass of the solid wax that was melted.
Steps:
1. Given: Mass of solid wax = 10 gm.
2. Using the key point mentioned above, we can conclude that the mass of the molten wax formed will also be 10 gm.
Final Answer:
The mass of the molten wax formed is 10 gm. Hence, the correct answer is C: 10 gm.

Periodic Change Example: Heartbeat

Periodic change refers to a phenomenon that occurs in a regular, repetitive pattern. Among the given options, the example of periodic change is the heartbeat (Option C). Here's a detailed explanation:

• Definition:




• Periodic change: A change that occurs in a regular, predictable pattern.





• Explanation:




• The heartbeat is a rhythmic contraction and relaxation of the heart muscles, which pumps blood throughout the body.


• It occurs in a steady, repetitive pattern.


• The heart contracts (systole) and then relaxes (diastole), creating a cyclic process.


• This cycle repeats continuously, maintaining blood circulation.





• Characteristics of Heartbeat:




• Occurs at regular intervals


• Has a consistent pattern


• Repeats continuously


• Essential for maintaining life





• Importance:




• Heartbeat is vital for supplying oxygen and nutrients to all organs and tissues in the body.


• It ensures the removal of waste products from the cells.


• Irregularities in the heartbeat can indicate health issues.


• Monitoring the heart's rhythm is crucial for diagnosing and treating various cardiac conditions.

Therefore, the heartbeat is an example of a periodic change due to its regular, repetitive nature.

Explanation:
When a few drops of petrol are poured on the palm, the following changes occur:
1. Evaporation: The drops of petrol start to evaporate, which means they transition from a liquid state to a gaseous state.
2. Heat Absorption: During the evaporation process, the petrol molecules gain energy from the surroundings, including the palm. This absorption of energy leads to cooling of the palm and gives a cool sensation.
Based on these observations, we can conclude that the change is an endothermic change because it involves the absorption of heat from the surroundings.
Therefore, the correct answer is D: Endothermic change.

Explanation:
The examples given in the question are:
1. The motion of planets around the sun
2. The motion of fan blades
3. The blinking of a traffic light
These examples are all related to periodic changes.
Periodic changes are changes that occur in a regular, repeating pattern. In these examples:
1. The motion of planets around the sun: Planets move in predictable orbits around the sun, completing their revolutions in fixed periods of time. This motion is periodic.
2. The motion of fan blades: When a fan is turned on, its blades rotate in a continuous, repetitive motion. Each rotation is a complete cycle, and the motion repeats itself. This motion is also periodic.
3. The blinking of a traffic light: Traffic lights have a specific pattern of blinking to indicate different signals, such as green for "go," yellow for "caution," and red for "stop." This blinking pattern repeats in a cycle, making it a periodic change.
Therefore, the correct answer is B: Periodic changes.

Endothermic Reaction:


Definition:

An endothermic reaction is a chemical reaction that requires energy to be absorbed from the surroundings in order to proceed.

Characteristics of Endothermic Reaction:

• Energy Absorption: In an endothermic reaction, energy is absorbed from the surroundings.


• Heat Absorption: The reaction absorbs heat from the surroundings, resulting in a decrease in temperature.


• Positive ΔH: The enthalpy change (ΔH) for an endothermic reaction is positive, indicating that energy is being taken in.


• Reactants: The energy absorbed is used to break the bonds in the reactants, resulting in the formation of new products.


• Examples: Some common examples of endothermic reactions include photosynthesis, melting of ice, and evaporation of water.

Explanation:

In an endothermic reaction, energy is absorbed from the surroundings, resulting in a decrease in temperature. This energy is used to break the bonds in the reactants, allowing the formation of new products. As a result, the enthalpy change (ΔH) for an endothermic reaction is positive, indicating that energy is being taken in.

It is important to note that an endothermic reaction still requires energy to proceed, but this energy is absorbed rather than released. This is in contrast to an exothermic reaction, where energy is released to the surroundings.

Overall, the correct answer is B: Energy is absorbed in an endothermic reaction.

Explanation:
Chemical reactions slow down in a cool environment:
- Many medicines and food articles contain chemical compounds that can degrade or break down over time.
- Keeping them in a cool environment helps slow down the chemical reactions, extending their shelf life and preserving their effectiveness.
Bacteria are frozen in a cool environment:
- While it is true that bacteria can grow and multiply in warmer temperatures, simply cooling the environment does not freeze or kill all bacteria.
- Some bacteria can still survive and grow in cooler temperatures, albeit at a slower rate.
- Therefore, the primary reason for storing medicines and food articles in a cool place is not to freeze or kill bacteria.
Microorganisms cannot survive in a cool environment:
- While some microorganisms, including certain bacteria, fungi, and viruses, may have difficulty surviving in cooler temperatures, not all microorganisms are affected the same way.
- Some microorganisms are adapted to cold environments and can still survive and multiply.
- Storing medicines and food articles in a cool place is not solely aimed at preventing the survival of microorganisms.
A and C both:
- Out of the given options, the most accurate and comprehensive answer is that storing medicines and food articles in a cool and dry place helps preserve them because chemical reactions slow down in a cool environment and microorganisms have difficulty surviving in a cool environment.
- This answer takes into account both the chemical stability of the products and the potential microbial growth, providing a more complete understanding of the preservation process.

The product formed by dissolving a substance into another is called a solution.

A solution is a homogeneous mixture formed when a solute is dissolved in a solvent. The solute is the substance that is being dissolved, while the solvent is the substance that dissolves the solute.

Here is a detailed explanation:

Definition of a

• A solution is a homogeneous mixture composed of two or more substances.


• The solute is the substance that is being dissolved, and the solvent is the substance that dissolves the solute.


• When a solute is dissolved in a solvent, the resulting mixture is called a solution.

Characteristics of a

• A solution is a homogeneous mixture, meaning that the composition is uniform throughout.


• It can be in the form of a liquid, gas, or solid.


• The solute particles are evenly dispersed and cannot be easily separated from the solvent.


• A solution can be separated into its components by physical means, such as evaporation or filtration.

Examples of Solutions:

• A sugar solution, where sugar (solute) is dissolved in water (solvent).


• Saltwater, where salt (solute) is dissolved in water (solvent).


• Carbonated drinks, where carbon dioxide gas (solute) is dissolved in a liquid (solvent).

In summary, a solution is the product formed when a substance (solute) is dissolved in another substance (solvent). It is a homogeneous mixture with uniform composition throughout. The solute particles are evenly dispersed and cannot be easily separated from the solvent.

Atoms combine through the interaction of electrons.

Explanation:

• The process of atom combination is known as chemical bonding.


• Chemical bonding occurs due to the interaction of electrons between atoms.


• Electrons are negatively charged particles that orbit around the nucleus of an atom.


• Atoms have a tendency to gain, lose, or share electrons to achieve a stable electron configuration.


• The interaction of electrons allows atoms to form chemical bonds and create compounds.


• There are different types of chemical bonds, including ionic bonds, covalent bonds, and metallic bonds.


• In ionic bonding, electrons are transferred from one atom to another, resulting in the formation of ions.


• In covalent bonding, electrons are shared between atoms to complete their outer electron shells.


• In metallic bonding, electrons are delocalized and shared among a lattice of metal atoms.

In summary, atoms combine through the interaction of electrons, which leads to the formation of chemical bonds and the creation of compounds.

Explanation:
Substances react with each other to form chemical bonds in order to become stable compounds. Here is a detailed explanation of why this happens:
1. Chemical reactions:
- Chemical reactions occur when substances interact with each other and undergo a change in their chemical composition.
- These reactions involve the breaking and formation of chemical bonds between atoms.
2. Stability:
- Atoms are constantly seeking stability by achieving a full outer electron shell.
- This can be done by either gaining, losing, or sharing electrons with other atoms.
- When atoms form chemical bonds, they become more stable as they achieve a full outer electron shell.
3. Formation of newer compounds:
- When substances react with each other, they combine to form newer compounds.
- These compounds have a different chemical composition and properties compared to the original substances.
- The formation of newer compounds occurs due to the rearrangement of atoms and the formation of new chemical bonds.
4. Increased or decreased energy:
- Chemical reactions involve a change in energy.
- Some reactions release energy, while others require energy input to proceed.
- The energy changes during a reaction are related to the breaking and formation of chemical bonds.
5. Decrease in energy:
- In some reactions, the formation of new chemical bonds results in a decrease in energy.
- This can occur when the newly formed compounds have a lower energy state compared to the original substances.
6. Increase in energy:
- In other reactions, the formation of new chemical bonds may require an input of energy.
- This can occur when the newly formed compounds have a higher energy state compared to the original substances.
7. Stability of compounds:
- The ultimate goal of chemical reactions is to form stable compounds.
- Stable compounds have lower energy states and are more likely to exist under normal conditions.
- These compounds have achieved a full outer electron shell, making them less reactive.
In conclusion, substances react with each other and form chemical bonds to become stable compounds. This process involves the formation of newer compounds, potential changes in energy, and the achievement of a more stable electron configuration.