Arrhenius Equation

Question 1

What is the trend between rate and temperature?

Answer 1

The rate constant for a reaction is not constant under all conditions - change with temperature
The rates of most reactions increase as temperature increases

Question 2

What is the Arrhenius equation

Answer 2

k= Ae^-Ea/RT

Many rate constants follow the Arrhenius equation when plotted as a function of temperature

Question 3

How can you find Ea and the pre exponential factor A?

Answer 3

k= Ae^-Ea/RT
1) take logs 
2) separate out and apply log rules to get:
lnk= lnA -Ea/R x 1/T
Compare this to a straight line 
Gradient=-Ea/R so rearrange to find Ea
Y intercept = lnA so remove ln to get A

Question 4

What graph would you plot to determine activation energy?

Answer 4

Plot lnK vs 1/T

Gradient is -Ea/R

Question 5

How does Ea determine temperature sensitivity?

Answer 5

At high values of Ea, this corresponds to a reaction that is very sensitive to changes of temperature
A low value of Ea, this corresponds to a reaction that is less sensitive to changes of temperature

Question 6

How can you predict k at a different temperature?

Answer 6

If you know k at one temp and Ea, you can work out k at different temp
lnk= lnA -Ea/RT
At unknown k, k=k' and T=T'
lnk'= lnA -Ea/RT'
Subtract this from equation 1
Simplify and make it equal k

Question 7

What is a reaction profile?

Answer 7

The reaction profile is a graph that shows the energy of the reaction system as the reaction proceeds