Reaction Rates And Equilibrium

Question 1

Equation for reaction rates (reactants+ products)?

Answer 1

reaction rate = ∆ [reactants]/ ∆ time
reaction rate = ∆ [products]/ ∆ time
[ ] means concentration
units= moldm-3 s-1

Question 2

For a reaction to occur what must happen (3 things)?

Answer 2

particles must collide
they must collide with sufficient energy
They must collide in the correct orientation

Question 3

What is activation energy?

Answer 3

Ea minimum energy for a reaction to take place?

Question 4

What does a lower Ea mean?

Answer 4

The lower the Ea the larger number of particles that can react and the faster the rate of reaction.

Question 5

What happens to rate of reaction if concentration is increased?

Answer 5

There are more particles in the same volume so the reactant particles are closer together so collisions are more frequent so the rate increases.

Question 6

What happens to rate of reaction if concentration is decreased?

Answer 6

There are less particles in the same volume so the reactant particles are further apart so collisions are less frequent so the rate decreases.

Question 7

What happens to rate of reaction if pressure is increased?

Answer 7

Same number of particles in a smaller volume so more frequent collisions between molecules so reaction rate is faster.

Question 8

What happens to rate of reaction if pressure is decreased?

Answer 8

Same number of particles in a larger volume so less frequent collisions between molecules so reaction rate is slower.

Question 9

How to work out rate of reaction from graph?

Answer 9

Draw a tangent from the curve make sure it doesn’t cross
draw a triangle from tangent
then work out the gradient change in y divided by the change in x

Question 10

What does a catalyst do?

Answer 10

increases the rate of reaction without being used up over the whole system
It allows a reaction to proceed via a different route with a lower activation energy. more frequent successful collisions

Question 11

In the presence of a catalyst more particles have?

Answer 11

More particles have the sufficient energy to react at the lower Ea increasing the reaction rate.

Question 12

Whats a homogeneous catalyst and whats an example of one?

Answer 12

A homogeneous catalyst is in the same state as the reactants (l,g,s,aq)
Ozone (O3) is catalyzed by chlorine free radicles.
O3 (g) + O (g) –> 2O2 (g) - its catlaysed by chlorine which is a gas so all state symbols are the same

Question 13

Whats a Heterogeneous catalyst and an example?

Answer 13

A heterogeneous catalyst is in a different state from the reactants.
harbor process- N2(g) + 3H2(g) ⇆ 2NH3 (g)
however its catalysed by iron which is a S

Question 14

What are the economic and environmental benefits of using a catalyst?

Answer 14

lower temperatures- lower the energy demand
less fossil fuels are burnt less CO2 produced
reduced cost because of reduced energy demand
less waste

Question 15

What are the economic and environmental limitations of using a catalyst?

Answer 15

initially expensive
eventually a catalysts surface can be poisoned
disposal of heavy metals can be difficult

Question 16

Boltzmann distribution facts?

Answer 16

distribution isn’t symmetrical
most particles have an energy that falls in a narrow range with fewer particles having having much more or less energy
line doesn’t cross the x-axis at higher energy it would only do this at infinite energy
the line starts at the origin showing particles have 0 energy
the total area under the curve us equal to the total number of gas particles.

Question 17

What does the shaded part after the Ea tell us?

Answer 17

These molecules have at least the Ea so when they collide they can react.

Question 18

What is the effect of increasing the temperature on the Boltzmann distribution?

Answer 18

More molecules with at least the Ea so more frequent successful collisions so faster rate of reaction. The Ea shifts to the right so higher temp

Question 19

What is the effect of decreasing the temperature on the Boltzmann distribution?

Answer 19

less molecules with at least the Ea so less frequent successful collisions so slower rate of reaction. The Ea shifts to the left and a lower temp

Question 20

Catalysts on the Boltzmann distribution?

Answer 20

doesn’t change the shape of the curve
greater proportion of molecules that exceed the new lower Ea when collision occurs more molecules will react and will form products
the rate of reaction increases.

Question 21

What does a reversible reaction mean?

Answer 21

Reaction can go forward and back.

Question 22

What is dynamic equilibrium?

Answer 22

closed system is isolated from the surroundings- nothing can enter/exit
both forward and reverse reaction are taking place.
At equilibrium:
as fast as the reactants are reacting to form products, the products are reacting to form reactants
the conc of the reactants and products remain the same
the equilibrium position is somewhere in between reactants and products

Question 23

What is equilibrium?

Answer 23

[the rate of forward reaction = the rate of backwards reaction]

Question 24

What does Le Chatelier mean?

Answer 24

what ever factor you change in a reversible reaction the reaction will do the opposite.

Question 25

What is the effect of increasing temperature on equilibrium?

Answer 25

if we increase the temperature in the system. Le Chatelier states that the system will reduce the temperature it does this by favoring the backwards reaction as it is endothermic and we say that equilibrium has shifted to the left so therefore more reactants are made.

Question 26

What is the effect of decreasing temperature on equilibrium?

Answer 26

if we decrease the temperature in the system. Le Chatelier states that the system will increase the temperature it does this by favoring the forward reaction as it is exothermic and we say that equilibrium has shifted to the right so therefore more products are made.

Question 27

Decomposition of phosphorus pentachloride- equilibrium exam practice
PCl5 ⇆ PCl3+ Cl2 +124kjmol

Answer 27

if we increase the temperature in the system. Le Chatelier states that the system will reduce the temperature it does this by favoring the forward exothermic reaction equilibrium has shifted to the right so therefore more products are made.

Question 28

Increasing pressure? collision theory

Answer 28

reduces the distance between particles so more frequent collisions

Question 29

Effects of pressure on equilibrium
2SO2 + O2 ⇆ 2SO3
Increasing pressure?

Answer 29

Le Chatelier states that the system will decrease the pressure there are less moles of gas in the products so it shifts the equilibrium to the right so more products are made.

Question 30

Effects of pressure on equilibrium
2SO2 + O2 ⇆ 2SO3
Decreasing pressure?

Answer 30

Le Chatelier states that the system will increase the pressure there are less moles of gas in the products so it shifts the equilibrium to the left so more reactants are made.

Question 31

equilibrium exam practice
PCl5 ⇆ PCl3+ Cl2
increasing pressure

Answer 31

Le Chatelier states that the system will decrease the pressure there are more moles of gas in the products so it shifts the equilibrium to the left so more reactants are made.

Question 32

equilibrium exam practice
PCl5 ⇆ PCl3+ Cl2
decreasing pressure

Answer 32

Le Chatelier states that the system will increase the pressure there are more moles of gas in the products so it shifts the equilibrium to the right so more products are made.

Question 33

What do catalysts do to equilibrium?

Answer 33

Catalysts speed up the rate of both forward and backwards reaction equally
the position of the equilibrium isn’t changed

Question 34

Why is a high temp better than low?

Answer 34

Low temperature may produce a reaction rate so slow that equilibrium may not be reached.

Question 35

Why is lower pressure better than high?

Answer 35

High pressure requires lots of energy so its expensive

Question 36

How to work out equilibrium constant?

Answer 36

Kc= [products] / [reactants]
If the molecule has a big number in front en 2NaCl2 it will go outside the [] as a power. if its after it goes inside
if there are multiple products or reactants you x them

Question 37

What does the Kc value tell us?

Answer 37

=1 equilibrium position is halfway between reactants and products
>1 equilibrium position favors the RHS/ products
<1 equilibrium position favors the LHS/ reactants