Rate and Kp

Question 1

What is the rate equation?

Answer 1

Change in conc/ change in time

Question 2

What are the units of rate?

Answer 2

mol dm-3 s-1

Question 3

What are orders of reaction related to?

Answer 3

After carrying out multiple experiments, rate can be proportional to the conc of certain reactants [A]

Question 4

How would you create a rate expression?

Answer 4

rate= k[A][B]^2

add a constant (k)
add the orders

Question 5

How do you find the overall order?

Answer 5

Just add up the orders

e.g first and second order makes 3

Question 6

What order is a reactant thats conc has no effect on rate?

Answer 6

zero order

-not included in the rate equation

Question 7

If a catalyst is used, do you include it in the rate expression with an order?

Answer 7

Yes
It always has an effect on rate so will never be a zero order

[H+]

Question 8

How would you calculate the constant ‘k’?

Answer 8

k= rate/ concs of products

e.g rate/ [A] [B]2

Question 9

How do you find rate on a graph?

Answer 9

Draw a tangent to the point you want on the curve, and do rise/ run to find the gradient which is equal to rate

Question 10

What does a 1st order reactant look like on a graph?

Answer 10

Straight line through the origin

/

Question 11

What does a 2nd order reactant look like on a graph?

Answer 11

Curved

)

Question 12

What does a zero order look like on a graph?

Answer 12

Horizontal line

__________

Question 13

What are elementary steps?

Answer 13

Basic steps in a reaction that cannot be broken down any further.

-Can take place at different rates
-Multiple steps to a reaction

Question 14

What are the 3 types of elementary steps and explain them?

Answer 14

1- Decomposition: one particle breaks into two
Cl2 —-> Cl+Cl

2- Substitution: particles collide and rearrange to form 2 completely different molecules.
Cl + CHCl3 —-> HCl + CCl3

3- Synthesis: particles collide and join as a single particle.
CCl3 + Cl —-> CCl4

Together these steps make a REACTION MECHANISM

Question 15

What is it called where a reaction only has one elementary step?

Answer 15

An elementary reaction

The reaction mechanism is just the overall equation.

Question 16

What is an intermediate?

Answer 16

Produced in one step and used up in another.

They are not shown in the overall equation.

Question 17

How do you make an overall equation from elementary steps?

Answer 17

1. Write out all equations
2. Cross out any intermediates
3. Add up duplicates of each other e.g. A+A. 2A

Question 18

How would you make a rate expression for a multi-step reaction?

Answer 18

-Do the same as a rate equation by crossing out intermediates.

-Take out any reactant that comes after the slowest step.

Only use reactants form before and during the slowest step.

Question 19

What is the rate-determining step?

Answer 19

The slowest step

Question 20

What is the rate expression useful for?

Answer 20

-Can work out what order the reactants are
-Use it along with the mechanism to determine the rate determining step.
-Use it to determine a correct mechanism

Question 21

What is the Arrhenius Equation?

Answer 21

K= Ae ^ -Ea/RT

A= arrhenius constant

Used to quantify a relationship between rate constant and temp

Question 22

Where is ‘e’ on a calculator? (arrhenius equation)

Answer 22

e and a square box

need to press shift

Question 23

What would help you find Ea form the Arrhenius equation?

Answer 23

ln (log)

ln(e^36)= 36

Question 24

How would you rearrange the Arrhenius equation?

Answer 24

Use ln of A and k

ln(k) = ln(A) -Ea/RT

Rearrange from there

e.g. Ea= RT( ln(A) - ln(k) )

Question 25

How would you find Ea on a graph using the Arrhenius equation?

Answer 25

1. Rearrange the equation in y=mx+c format —> ln(k) = -Ea/R. x 1/T. + ln(A)
2. On a graph y axis= ln(k) and x axis= 1/T
3. In y=mx+c, ‘m’ is the gradient therefore -Ea/R is the gradient
4. Ea = R x (-gradient). in KJ mol-1

Question 26

What is the Kp equation?

Answer 26

Kp= pressure of products/ pressure of reactants

Question 27

What is partial pressure?

Answer 27

You have a mixture of A and B in a container…

Partial pressure is if A were in that same container on its own

Question 28

What is partial pressure represented as?

Answer 28

Capital P with tiny compound

e.g. Po2
(P is big)
(O2 is small)

Question 29

What is the mole fraction equation?

Answer 29

mol fraction of gas A= n.o of mol gas A/. total n.o of mol in mixture

Question 30

How do you calculate partial pressure?

Answer 30

Partial pressure of A= total pressure x mol fraction of A

Question 31

How do you express Kp?

Answer 31

pressure in round brackets

Kp= pressure products/ pressure reactants

e.g. Kp= (Po2)^2 (Po2). /. (Po3)

Question 32

How would you answer a Kp question?

Answer 32

1. Write out expression
2. Find mol of each at equilibrium using an ICE table
3. Find mole fraction of each gas
4. Find partial pressures
5. Plug in values to Kp expression

Question 33

What effects Kp?

Answer 33

Only temperature