C6 Rate of Reaction (Part 2)

Question 1

What is a catalyst and how
does it work? How does it
affect the reaction profile?

Answer 1

A catalyst changes the rate of reaction but is not used up. It increases rate of
reaction by providing a different pathway for the reaction that has a lower
activation energy. The reaction profile for a catalysed reaction will have a lower
maximum of the curve (lower activation energy).

Question 2

What is an enzyme?

Answer 2

An enzyme is a molecule that acts as a catalyst in a biological system.

Question 3

What is a reversible reaction?

Answer 3

A reversible reaction occurs when the products of a reaction can react backwards
to produce the original reactants

Question 4

When is dynamic

equilibrium reached?

Answer 4

In a closed system, when the forward and reverse reactions occur at the same rate
and the concentrations of reactants and products remain constant.

Question 5

Describe Le Chatelier’s

Principle

Answer 5

If a system is at equilibrium and a change is made to any of the conditions, then
the system responds to counteract change and restore the equilibrium.

Question 6

Describe the effect of
changing the concentration of
reactant and product on the
position of the equilibrium

Answer 6

If the concentration of one of the reactants or products is changed, the system is
no longer at equilibrium and the concentrations of all the substances will change
until equilibrium is reached again. If the concentration of a reactant is increased,
more products will be formed until equilibrium is reached again. If the
concentration of a product is decreased, more reactants will react until equilibrium
is reached again.

Question 7

Describe the effect of
changing temperature on the
position of the equilibrium

Answer 7

If the temperature of a system at equilibrium is increased:
• the relative amount of products at equilibrium increases for an endothermic
reaction
• the relative amount of products at equilibrium decreases for an exothermic
reaction.

Question 8

Describe the effect of
changing pressure on the
position of the equilibrium

Answer 8

An increase in pressure causes the equilibrium position to shift towards the side
with the smaller number of molecules as shown by the symbol equation for that
reaction. A decrease in pressure causes the equilibrium position to shift towards
the side with the larger number of molecules as shown by the symbol equation
for that reaction. Pressure has no effect on the reactions where the numbers of
gas molecules are equal on both sides of the equation.

Question 9

Describe the effect of a
catalyst on the position of the
equilibrium

Answer 9

No effect.
It just speeds up both forward and backward reactions equally.
i.e. equilibrium is achieved faster.