DEPARTMENT OF NATURAL SCIENCE SUBJECT: CHEMISTRY

The rate of a chemical reaction is a measure of how fast the reaction occursThe rate of a chemical reaction is a measure of how fast the reaction occursThe rate of a chemical reaction is a measure of how fast the reaction occursThe rate of a chemical reaction is a measure of how fast the reaction occursThe rate of a chemical reaction is a measure of how fast the reaction occursThe rate of a chemical reaction is a measure of how fast the reaction occurs

DEPARTMENT OF NATURAL SCIENCE

DUY TAN UNIVERSITY

SUBJECT: CHEMISTRY

RATE OF A CHEMICAL REACTION

Reaction rate

1 Definition

2015

The rate of a chemical reaction is a measure of how fast the reaction occurs.

Generic reaction:

aA + bB → cC + dD

Reaction rate

The rate of a chemical reaction is measured as a change in the amounts of reactants or products divided by the change in time

Rate

Reaction rate

The equation for a reaction is:

2NO2(g) + H2O(g) + 1/2O2(g) → 2HNO3 (g)

Which one of the following is not numerically equal to the others?

Answer: B

Exercise 1

[ 2 ]

1

2

NO A

t

∆

−

∆

[ ]2

1

2

O B

t

∆

−

∆

[ 2 ]

C

t

∆

−

∆

1 2

HNO D

t

∆

∆

For example

Consider the following balanced chemical equation

Reaction rate

H2O2 (aq) + 3I - (aq) + 2H + (aq) → I3 - (aq) + 2H2O(l)

In the first 10,0 second of the reaction, the concentration of I- dropped from 1.000M to 0,868M.

Calculate the average of the reaction rate in this time interval.

2 The rate Law:

The effect of concentration

Consider this reaction:

aA + bB → cC + dD

Rate = k[A]m [B] n

k: rate constant

m: the reaction order with respect to A

n: the reaction order with respect to B

m + n: the overall order

The rate law for any reaction must always be determined by experiment.

2 The rate Law:

The effect of concentration

For example:

2NO2(k) + F2(k) → 2NO2F(k)

Rate = k[NO2][F2]

2 The rate Law:

The effect of concentration

EXAMPLE

Consider the reaction and the obtained rate / concentration data:

A(aq) + B(aq) → C(aq)

3 The Effect of Temperature on Reaction Rate

The Arhenius equation

R: the gas constant (8.314 J/mol.K)

A: constant called the frequency factor

Ea : the activation energy (is an energy barrier or hump that must be

surmounted for the reactants to be transformed into products)

RT Ea

k A e = −

Thank you