Chemical Kinetics and Rate
Lecture No. 1
Chemical Kinetics
1.1 The Rate of a Reaction
Chemical Kinetics is the area of Chemistry that is concerned with the speed, rate or mechanism at which a chemical reaction occurs.
Reaction Rate is the change in the concentration of a reactant or product with time (i.e. M/s). It measures how fast a reactant is consumed and how fast a product is formed.
1.2 WRITING RATE EXPRESSIONS
Consider the following hypothetical reaction. A + 2B ( 3C + D Rate = - rate of consumption of A = -[pic]rate of consumption of B = [pic] rate of formation of C = rate of formation of D
In terms of concentration changes Average rate with respect to A Rate = [pic] Average rate with respect to B Rate = [pic] Average rate with respect to C Rate = [pic] Average rate with respect to D Rate = [pic] Rate = -[pic] = -[pic] = [pic] = [pic]
Notes: • The minus sign makes the value of the rate positive (since A2 < A1). • The division of each concentration by the coefficient from the balanced equation makes all of the above rates equal. • The unit of rate could be moles per liter per second (mol L-1s-1) or Ms-1
Example: Write the rate expressions of the following reaction in terms of the reactants and products H2(g) + I2(g) ( 2HI(g)
Strategy: Each change in concentration term is divided by the corresponding stoichiometric coefficient. Terms involving reactants are preceded by a minus sign.
Solution: Rate = [pic]
Practice Exercise 1. Because it has a nonpolluting combustion product (water vapor), hydrogen gas is used as fuel for space shuttles and may someday be used by earth-bound engines: 2H2(g) + O2(g) ( 2H2O(g) a. Express the rate in terms of changes in [H2], [O2] and [H2O] with time. b. When [O2] decreases at 0.23 mol/L-s, at what rate does [H2O] increase?
Practice Exercise 2. Consider the reaction :
Chemical Kinetics
1.1 The Rate of a Reaction
Chemical Kinetics is the area of Chemistry that is concerned with the speed, rate or mechanism at which a chemical reaction occurs.
Reaction Rate is the change in the concentration of a reactant or product with time (i.e. M/s). It measures how fast a reactant is consumed and how fast a product is formed.
1.2 WRITING RATE EXPRESSIONS
Consider the following hypothetical reaction. A + 2B ( 3C + D Rate = - rate of consumption of A = -[pic]rate of consumption of B = [pic] rate of formation of C = rate of formation of D
In terms of concentration changes Average rate with respect to A Rate = [pic] Average rate with respect to B Rate = [pic] Average rate with respect to C Rate = [pic] Average rate with respect to D Rate = [pic] Rate = -[pic] = -[pic] = [pic] = [pic]
Notes: • The minus sign makes the value of the rate positive (since A2 < A1). • The division of each concentration by the coefficient from the balanced equation makes all of the above rates equal. • The unit of rate could be moles per liter per second (mol L-1s-1) or Ms-1
Example: Write the rate expressions of the following reaction in terms of the reactants and products H2(g) + I2(g) ( 2HI(g)
Strategy: Each change in concentration term is divided by the corresponding stoichiometric coefficient. Terms involving reactants are preceded by a minus sign.
Solution: Rate = [pic]
Practice Exercise 1. Because it has a nonpolluting combustion product (water vapor), hydrogen gas is used as fuel for space shuttles and may someday be used by earth-bound engines: 2H2(g) + O2(g) ( 2H2O(g) a. Express the rate in terms of changes in [H2], [O2] and [H2O] with time. b. When [O2] decreases at 0.23 mol/L-s, at what rate does [H2O] increase?
Practice Exercise 2. Consider the reaction :