Arrhenius Equation Flashcards
What is the Arrhenius equation?
K= Ae ^ -Ea/RT
What does the Arrhenius equation link?
Links the k ( rate constant) with temperature
What are the different parts of the Arrhenius equation?
K= rate constant
Ea= activation energy Jmol-1
T= temp in k
R= gas constant 8.31 JK-1 mol-1
A= pre exponential factor, same units as K
What happens to rate when there is a high activation energy?
High activation energy= molecules are inhibited from colliding successfully = slow rate of reaction = low rate constant
Describe how the Arrhenius equation proves the effect of a high activation energy on the rate constant?
High activation energy= fraction gets bigger with large Ea= power is more negative, so a bigger negative number= lower value of K
What is the effect on K if there is a low activation energy?
There will be a higher rate constant= as there will be more successful collisions between particles
How does the Arrhenius equation prove the effect on rate after a low activation energy?
Fraction gets smaller with a lower activation energy= power is less negative= so value of K increases
What is the effect of a higher temperature on the value of K?
A higher temperature= higher value of K= more kinetic energy for molecules to have successful collisions = increased rate of reaction
How does the Arrhenius equation prove the effect of a higher temperature on the value of K?
Larger temperature= fraction is smaller= power becomes less negative = larger k value
how do you use the Arrhenius equation to work out the activation energy ?
- Use and sub the number into the equation : In (k)= -Ea/RT + In (A)
- Then take away : In(A) and RT away from the rate number on the other side
- Then if the remains number is negative, cancel the sign and make it positive.
- Convert units from Jmol-1 to kJmol-1 by dividing by 1000
How would you use the Arrhenius equation to work out the pre - exponential factor A?
- Use the In(K) = -Ea/ RT + In (A) equation and insert the number in (makes sure all units are correct)
- Then once K has been worked out, them add -Ea/Rt from K
3.then to get A you use the value of K in inverse =
e^ K= A
- A also has the same units as rate
Show how the Arrhenius equation can be re arranged to the same as y= m x + c?
In (K)= -Ea/ R . 1/T + In A
Y= m X + C
Y term = In (k)
X term= 1/t
Gradient= -Ea/R
Y intercept= In (A)
How do you calculate the activation energy from a Arrhenius plotted graph?
- You have to calculate the gradient of the graph
= change in Y/ change in X - Then multiply the value by R
How do you work out ln (A) from an Arrhenius plotted graph?
- You pick a point on the graph and insert all numbers into the equation: In (K) = -Ea/ RT + In (A) . To get t, just use ur 1/T value of the graph
- Then once the K value has been worked out add on the value of -Ea/RT.
- Then use the inverse to get A, which is e^ k.
- The units are the same as rates
