5.1.5: The effect of temperature on rate constants

Question 1

What does rate of reaction depend on?

Answer 1

The rate constant and the concentrations of the reactants present in the rate equation.
-The larger the value of K, the faster the reaction.

Question 2

Why does increasing temperature increase the rate of reaction?

Answer 2

• More energy to molecules
• Collisions more frequent
• More collisions exceed activation energy of the reaction
• Raising temp. speeds up the rate of most reactions by increasing the rate constant, k.

Question 3

For many reactions, the rate approx. doubles for each 10 degrees increase in temperature. What does this reflect?

Answer 3

This reflects the greater number of reacting particles that exceed the activation energy.

Question 4

Typically, what would doubling the rate have on the rate constant k?

Answer 4

Typically, doubling the rate would double k.

Question 5

What is the Arrhenius equation used to describe, mathematically?

Answer 5

The exponential relationship between the rate constant and the temperature.

Question 6

What is the Arrhenius equation?

Answer 6

k=Ae^-Ea/RT
k=rate constant 
A=pre-exponential factor
Ea=activation energy 
R=gas constant (8.314)
T=temp. in kelvins (+273)

Question 7

What needs to happen for particles to be able to react?

Answer 7

-Molecules have to collide with enough energy to overcome the activation energy.

Question 8

What does the Arrhenius equation tell us?

Answer 8

• Temperature, T, and the rate constant, k, are related exponentially.
• As temperature increases the rate constant increases.

Question 9

What effect does increasing adding a catalyst have on the value of k.

Answer 9

• Adding a catalyst provides an alternative reaction path with a lower activation energy, Ea.
• This increases the rate constant, k.

Question 10

What is the Arrhenius equation after you take logs?

Answer 10

ln(k) = ln(A) - (Ea/R) x (1/T)

Question 11

How do you create an Arrhenius plot?

Answer 11

• A given reaction is carried out at varying temperatures and the value of the rate constant is calculated for each temperature.
• A graph for k can be plotted against 1/T.

Question 12

What can the Arrhenius plot be used to identify?

Answer 12

ln(k) = ln(A) - (Ea/R) x (1/T)
y = c m x
(intercept) (gradient)
-A: The intercept on the graph is equal to ln(A).
-The activation energy, Ea: the gradient is equal to (-Ea/R)