Reaction Rates and Collision Theory

Question 1

What is the equation for reaction rates?

Answer 1

/\reactants / /\time
/\products / /\ time

Question 2

What are the units for reactions rates?

Answer 2

mol dm^-3 s^-1

Question 3

What is Activation Energy?

Answer 3

The minimum amount of energy in order for a reaction to occur

Question 4

How does concentration affect reaction rate?

Answer 4

Increasing the concentration mean an increase in the number of particles within the same volume of space, so there are more frequent collisions so a faster rate of reaction

Question 5

How does pressure affect reaction rate?

Answer 5

An increased pressure means the same number of particles in a smaller volume of space. This means there will be more frequent collisions so a faster rate of reaction

Question 6

How does Temperature affect reaction rate?

Answer 6

Increasing temperature increases the energy of the molecules, so they move faster meaning more frequent collisions

More particles have the activation energy so there are more successful collisions

Question 7

How does each factor affect The Boltzman Distribution?

Answer 7

Increase Temperature: increase average E, more molecules with Ea, lower peak

Decrease Temperature: decrease average E, less molecules with Ea, higher peak

Question 8

How do catalysts affect reaction rate?

Answer 8

Increase reaction rate, provide an alternative reaction pathway with a lower activation energy - not used up regenerated

Question 9

What is heterogeneous and a homogenous catalyst?

Answer 9

Heterogeneous: Catalyst in a different state to the reactants
Homogeneous: Catalyst in the same state to the reactants

Question 10

Give some examples catalyst.

Answer 10

Fe (s)
H2SO5 (aq)
Pt (s)
HF (g)
Ni (s)

Question 11

What are the advantages and disadvantages of catalysts?

Answer 11

Advantages: faster reactions, can be reused, use lower temp, reduce energy cost and pollution, less waste, atom economy and % yield improve (sometimes)

Disadvantages: initially expensive, eventually catalyst surface can be poisoned, disposal of heavy metals can be difficult

Question 12

What is the equation for rate equations?

Answer 12

rate = k[reactant][reactant]

Question 13

What is the definition for the order of a reactant in rate equations?

Answer 13

The order of a reactant is the power its concentration is raised to in the rate equation

Question 14

How do you calculate the order of reactants in rate equations?

Answer 14

By how it effects the reaction rate (slowest reaction)
[reactants] x X , [rest of reactants] are constant, rate x A = X^a
order of [reactant] is a

Question 15

What are the axis labels for reaction rate graphs?

Answer 15

x axis - concentration
y axis - rate

Question 16

What does it mean if the rate-concentration graph is a flat line?

Answer 16

zero order - changing concentration has not effect on rate

Question 17

What does it mean if the rate-concentration graph is a straight line through the origin?

Answer 17

order 1 - the concentration is directly proportional to the rate

Question 18

What does it mean if the rate-concentration graph curves upwards or concentration is squared?

Answer 18

order 2 - [reactant]^2 is directly proportional to rate

Question 19

How do you plot a rate-concentration graph?

Answer 19

Plot the points where the other values remain constant

Question 20

How do you solve k in reaction rates?

Answer 20

k = rate/[reactants]

Question 21

What is the definition of half life?

Answer 21

time for concentration of a reactant to fall to half the original value

Question 22

How do half lives change for order 0, 1 and 2?

Answer 22

0 - goes down each time
1 - remains constant
2 - half-life increases (not a rule)

Question 23

How can you calculate k (rate constant)? (2 ways)

Answer 23

straight line graph - y = mx + c where m=k
curved - k = (ln2)/t1/2