Chemical Kinetics PPT Chemistry Class 12

 Page 1


15 Chemical Kinetics
1
15 Chemical Kinetics
Chemical kinetics: the study of reaction rate, ? a quantity
conditions affecting it,
the molecular events during a chemical reaction (mechanism), and 
presence of other components (catalysis).
Factors affecting reaction rate:
Concentrations of reactants
Catalyst
Temperature
Surface area of solid reactants or catalyst
What quantities do we study regarding chemical reactions?
Page 2


15 Chemical Kinetics
1
15 Chemical Kinetics
Chemical kinetics: the study of reaction rate, ? a quantity
conditions affecting it,
the molecular events during a chemical reaction (mechanism), and 
presence of other components (catalysis).
Factors affecting reaction rate:
Concentrations of reactants
Catalyst
Temperature
Surface area of solid reactants or catalyst
What quantities do we study regarding chemical reactions?
15 Chemical Kinetics
2
Reaction Rate Defined
Reaction rate: changes in a concentration 
of a product or a reactant per unit time.
?[ ] concentration
Reaction rate = ——
? t
[ ]
t
?[ ]
?t
change
Define reaction rate and explain
Average reaction rate
Instantaneous reaction rate
(2 tangents shown)
Initial reaction rate
Page 3


15 Chemical Kinetics
1
15 Chemical Kinetics
Chemical kinetics: the study of reaction rate, ? a quantity
conditions affecting it,
the molecular events during a chemical reaction (mechanism), and 
presence of other components (catalysis).
Factors affecting reaction rate:
Concentrations of reactants
Catalyst
Temperature
Surface area of solid reactants or catalyst
What quantities do we study regarding chemical reactions?
15 Chemical Kinetics
2
Reaction Rate Defined
Reaction rate: changes in a concentration 
of a product or a reactant per unit time.
?[ ] concentration
Reaction rate = ——
? t
[ ]
t
?[ ]
?t
change
Define reaction rate and explain
Average reaction rate
Instantaneous reaction rate
(2 tangents shown)
Initial reaction rate
15 Chemical Kinetics
3
Expressing reaction rates
For a chemical reaction, there are many ways to express the reaction 
rate. The relationships among expressions depend on the equation.
Note the expression and reasons for their relations for the reaction 
2 NO + O
2 
(g) = 2 NO
2
(g)
?[O
2
] 1 ?[NO]       1   ?[NO
2
] 
Reaction rate = – ——— = – — ———— = — ———
? t 2 ? t 2      ? t
Make sure you can write expressions for any reaction and figure out 
the relationships. For example, give the reaction rate expressions for
2 N
2
O
5
= 4 NO
2
+ O
2
How can the rate expression be unique and universal?
Page 4


15 Chemical Kinetics
1
15 Chemical Kinetics
Chemical kinetics: the study of reaction rate, ? a quantity
conditions affecting it,
the molecular events during a chemical reaction (mechanism), and 
presence of other components (catalysis).
Factors affecting reaction rate:
Concentrations of reactants
Catalyst
Temperature
Surface area of solid reactants or catalyst
What quantities do we study regarding chemical reactions?
15 Chemical Kinetics
2
Reaction Rate Defined
Reaction rate: changes in a concentration 
of a product or a reactant per unit time.
?[ ] concentration
Reaction rate = ——
? t
[ ]
t
?[ ]
?t
change
Define reaction rate and explain
Average reaction rate
Instantaneous reaction rate
(2 tangents shown)
Initial reaction rate
15 Chemical Kinetics
3
Expressing reaction rates
For a chemical reaction, there are many ways to express the reaction 
rate. The relationships among expressions depend on the equation.
Note the expression and reasons for their relations for the reaction 
2 NO + O
2 
(g) = 2 NO
2
(g)
?[O
2
] 1 ?[NO]       1   ?[NO
2
] 
Reaction rate = – ——— = – — ———— = — ———
? t 2 ? t 2      ? t
Make sure you can write expressions for any reaction and figure out 
the relationships. For example, give the reaction rate expressions for
2 N
2
O
5
= 4 NO
2
+ O
2
How can the rate expression be unique and universal?
15 Chemical Kinetics
4
Calculating reaction rate
The concentrations of N
2
O
5
are 1.24e-2 and 0.93e-2 M at 600 and 
1200 s after the reactants are mixed at the appropriate temperature. 
Evaluate the reaction rates for
2 N
2
O
5
= 4 NO
2
+ O
2
Solution:
(0.93 – 1.24)e-2 – 0.31e-2 M
Decomposition rate of N
2
O
5
= – ———————— = – ——————
1200 – 600 600 s
= 5.2e-6 M s
-1
.
Note however, 
rate of formation of NO
2
= 1.02e-5 M s
-1
.
rate of formation of O
2
= 2.6e-6 M s
-1
.
The reaction rates are 
expressed in 3 forms
Be able to do this type problems
Page 5


15 Chemical Kinetics
1
15 Chemical Kinetics
Chemical kinetics: the study of reaction rate, ? a quantity
conditions affecting it,
the molecular events during a chemical reaction (mechanism), and 
presence of other components (catalysis).
Factors affecting reaction rate:
Concentrations of reactants
Catalyst
Temperature
Surface area of solid reactants or catalyst
What quantities do we study regarding chemical reactions?
15 Chemical Kinetics
2
Reaction Rate Defined
Reaction rate: changes in a concentration 
of a product or a reactant per unit time.
?[ ] concentration
Reaction rate = ——
? t
[ ]
t
?[ ]
?t
change
Define reaction rate and explain
Average reaction rate
Instantaneous reaction rate
(2 tangents shown)
Initial reaction rate
15 Chemical Kinetics
3
Expressing reaction rates
For a chemical reaction, there are many ways to express the reaction 
rate. The relationships among expressions depend on the equation.
Note the expression and reasons for their relations for the reaction 
2 NO + O
2 
(g) = 2 NO
2
(g)
?[O
2
] 1 ?[NO]       1   ?[NO
2
] 
Reaction rate = – ——— = – — ———— = — ———
? t 2 ? t 2      ? t
Make sure you can write expressions for any reaction and figure out 
the relationships. For example, give the reaction rate expressions for
2 N
2
O
5
= 4 NO
2
+ O
2
How can the rate expression be unique and universal?
15 Chemical Kinetics
4
Calculating reaction rate
The concentrations of N
2
O
5
are 1.24e-2 and 0.93e-2 M at 600 and 
1200 s after the reactants are mixed at the appropriate temperature. 
Evaluate the reaction rates for
2 N
2
O
5
= 4 NO
2
+ O
2
Solution:
(0.93 – 1.24)e-2 – 0.31e-2 M
Decomposition rate of N
2
O
5
= – ———————— = – ——————
1200 – 600 600 s
= 5.2e-6 M s
-1
.
Note however, 
rate of formation of NO
2
= 1.02e-5 M s
-1
.
rate of formation of O
2
= 2.6e-6 M s
-1
.
The reaction rates are 
expressed in 3 forms
Be able to do this type problems
15 Chemical Kinetics
5
Determine Reaction Rates
To measure reaction rate, we measure the concentration 
of either a reactant or product at several time intervals.
The concentrations are measured using spectroscopic 
method or pressure (for a gas). For example, the total 
pressure increases for the reaction:
2 N
2
O
5 
(g) ? 4 NO
2 
(g) + O
2
(g)
Because 5 moles of gas products are produced from 2 
moles of gas reactants. For the reaction
CaCO
3 
(s) ? CaO(s) + CO
2
(g)
The increase in gas pressure is entirely due to CO
2
formed.
barometer