C6 - The Rate and Extent of Chemical Change

Question 1

What is the rate of a reaction?

Answer 1

How fast the reactants are changed into products.

Question 2

If the reaction time graph is steep, what is the rate of reaction?

Answer 2

Fast.

Question 3

What does a chemical reaction depend on?

Answer 3

1) The frequency of particle collisions.
2) The energy transferred in a collision.

Question 4

What factors affect rate of reaction?

Answer 4

1) Temperature.
2) The concentrate of a solution or the pressure of a gas.
3) Surface area.
4) Presence of a catalyst.

Question 5

What happens when you increase the temperature?

Answer 5

• The particles move faster.
• They collide more frequently.
• They have more energy.

Question 6

How does increasing the concentration and pressure affect the rate of a reaction?

Answer 6

• There are more particles.
• The collisions are more frequent.

Question 7

How does increasing the surface area increase the rate of reaction?

Answer 7

• This increases the surface area to volume ratio.
• Therefore particles have more area to work, so there will be more frequent collisions.

Question 8

How does using a catalyst increase the rate of reaction?

Answer 8

Catalysts decrease the activation energy by providing an alternative reaction pathway with a lower activation energy.

Question 9

How do reversible reactions reach equilibrium?

Answer 9

• As reactants react, their concentrations fall, so the forward reaction will slow down.
• As more products are made, their concentrations rise so the backward reaction will speed up.
• Eventually, both reactions will occur at the same time which is called equilibrium.

Question 10

What is dynamic equilibrium?

Answer 10

Both reactions are still happening, but there is no overall effect as they are happening at the same time.

Question 11

What does the position of equilibrium depend on?

Answer 11

1) Temperature.
2) Pressure (gas only).
3) Concentration.

Question 12

Explain the thermal decomposition of hydrated copper sulfate.

Answer 12

• If you heat blue hydrated copper(II) sulfate crystals, it drives the water off and leaves white anhydrous copper(II) sulfate powder. This is endothermic.
• If you add a couple of drops of water to the white powder, you get the blue crystals back again. This is exothermic.

Question 13

What is Le Chatelier’s Principle?

Answer 13

If the conditions of a reversible reaction at equilibrium change, the system will counteract the change.

Question 14

What happens to the position of equilibrium if the temperature is changed?

Answer 14

• If you decrease the temperature, the equilibrium will shift in the exothermic direction to produce more heat.
• If you increase the temperature, the equilibrium will shift in the endothermic direction to decrease the heat.

Question 15

What happens to the position of equilibrium if pressure is changed?

Answer 15

• Changing pressure only affects an equilibrium involving gases.
• If the pressure increases, the equilibrium shifts to the direction where there are fewer molecules of gas to try and reduce the pressure.
• If the pressure decreases, the equilibrium shifts to the direction where there are more molecules of gas to try and increase the pressure.

Question 16

What happens to the position of equilibrium if the concentration is changed?

Answer 16

• If the concentration changed, the system is no longer at equilibrium so the system responds to bring itself back to equilibrium again.
• If the concentration of the reactants increases, the system makes more products to try and decrease it.
• If the concentration of products decreases, the system tries to increase it by reducing the amount of reactants.