reactants products

• Formulate an definition of reaction rate.  • Identify variables used to monitor reaction ratesExamples: pressure, temperature, pH, conductivity  • Perform calculations to measure average and

instantaneous rate.  • Compare rates given experimental rate data and

reaction stoichiometry.

Additional KEY Terms

Kinetics

Branch of chemistry that studies the speed or rate with which chemical reactions occur.

Some reactions do not occur in one simple step. Some occur in several more complex steps.

Kinetics includes studying the steps, or mechanism, of a chemical reaction.

Rate - refers to the speed of the reaction• How fast reactants are used or products form.

A(s) + B(l) C(g) + heat

exothermic

A(s) + heat C(g) + B(l)

endothermic

(°C/min)(kPa/s or mmHg/s)

(g/min)Colour, pH, conductivity (over time).

Rate can be measured using different methods depending on the reaction:

A(s) + B(l) C(g) + heat

*We will only use concentration change with time.

Rate = Δ[A] Δt

Rate = [A]final - [A]initial tfinal - tinitial

Average Rate is described as total change in concentration of reactant or product over time.

Reactions have quick initial rates, but slow down over

time.

Con

cent

rati

on

Time

Instantaneous rate - rate at a specific time. Determined by calculating the slope of the line tangent to a point on the curve.

Calculating Average Rate

A B

Time (s) Concentration of B (mol/L)

0.0 0.010.0 0.3020.0 0.5030.0 0.6040.0 0.6550.0 0.67

a. What is the average rate over the entire 50 seconds?

b. What is the average rate for the interval 20 s to 40 s?

Decomposition of nitrogen dioxide produces nitrogen monoxide and oxygen:

2 NO2 (g) 2 NO (g) + O2 (g)

Time(s)

[NO2](mol/L

[NO](mol/L)

[O2](mol/L)

0.0 0.100 0.00 0.00

100 0.066 0.034 0.017

200 0.048 0.052 0.026

300 0.038 0.062 0.031

400 0.030 0.070 0.035

a. Ave. rate of decomposition of NO2 over 400 s.

Actual value is 1.75 x 10-4 mol/L·s

Rate is always expressed

as a positive value.

b. Ave. rate of production of O2 over 400 s.

Rates can be predicted from reaction stoichiometry.

2 NO2 (g) 2 NO (g) + O2 (g)

· rate of decomposition of NO2 is equal to the production of NO - molar coefficients are 1:1.

= Δ[O2] Δt

Δ[NO] Δt

2 = Δ[O2] Δt

Δ[NO2] Δt

½

2 NO2 (g) 2 NO (g) + O2 (g)

· rate of production of O2 is half of the NO - molar coefficients are 1:2.

What is the rate of production of C and the rate of disappearance of B if A is used up at a rate of 0.60 mol/Ls?

2 A + B 3 C

0.60 mol/L·s A2 mol A

1 mol B= 0.30 mol/L·s B

0.60 mol/L·s A2 mol A

3 mol C= 0.90 mol/L·s C

CAN YOU / HAVE YOU?

• Formulate an definition of reaction rate.  • Identify variables used to monitor reaction ratesExamples: pressure, temperature, pH, conductivity  • Perform calculations to measure average and

instantaneous rate.  • Compare rates given experimental rate data and

reaction stoichiometry.