The rate and Extent of Chemical Change

Question 1

the equation for the rate of reaction?

Answer 1

Amount of reactant used or amount of product formed

divided by

Time (seconds)

Question 2

definition of turbidity?

Answer 2

cloudiness

Question 3

When do chemical reactions occur?

Answer 3

when reacting particles collide with each other with sufficient energy

Question 4

What is the activation energy?

Answer 4

the minimum amount of energy required to cause a reaction

Question 5

What are the factors that affect the rate of reaction?

Answer 5

• Temperature
• concentration of reactants in solution
• pressure of reacting gases
• surface area of solid reactants
• the presence of catalysts

Question 6

How does temperature affect the rate of reaction?

Answer 6

• high-temperature cause particles to move more quickly
• faster they move, the more energy they will have
• they will collide more often with greater energy so more collisions are successful

Question 7

How does concentration and pressure affect the rate of reaction?

Answer 7

• at higher concentrations, the particles are crowded close together
• they collide more often = more successful collision
• Increasing pressure of reacting gases also increases the frequency of collisions

Question 8

How does surface area affect the rate of reaction?

Answer 8

• small pieces of solid reactant have a large surface area

- more particles are exposed and available for collisions, so there are more collisions and faster reactions

Question 9

What is a catalyst?

Answer 9

a substance that increases the rate of a chemical reaction without being used up in the process

Question 10

Why are catalysts good?

Answer 10

• reduces the activation energy
• makes more collisions successful
• speeds up the reaction
• provides an alternate reaction pathway
• provides a surface for the molecules to attach to, increases the chance of collisions

Question 11

How does increasing the rates of chemical reactions help the industry?

Answer 11

it reduces costs

Question 12

What increases the frequency of collisions and therefore increases the rate of reaction?

Answer 12

Increasing :

• concentration of reactants in solution
• the pressure of reacting gases
• the surface area od solid reactants

Question 13

What happens in a reversible reaction?

Answer 13

the products can react to produce the original reactants

Question 14

Describe why the rate of the forward and backward reaction changes during reversible reactions

Answer 14

As reactants reactm their concentrations fall, so the forward reaction will slow down

as more products re made their concentrations rise, the backward reaction will speed uo

Question 15

What is a closed system?

Answer 15

no reactants are added, no products are removed

Question 16

What happens when a reversible reaction happens in a closed system?

• describe what a dynamic equilibrium is

Answer 16

a dynamic equilibrium is eventually achieved = the rate of the forward reaction is equal to the rate of the backward reaction

= concentrations of reactants and products have reached a balance and wont change

• this doesnt mean thte amounts of reactants and products are equal

Question 17

What does it mean when the equilibrium lies to the left/right?

Answer 17

left = concentration of products are greater

right = concentration of reactants greater

Question 18

What is le chatelier’s principle?

Answer 18

when conditions of a reaction in equilibrium are changed the reaction will do everything it can to counteract the change

Question 19

What happens when the temperature of a system at equilibrium is increases or decreases in an EXOTHERMIC reaction?

and why

Answer 19

decrease = increased yield as the equilibrium will move in the exothermic direction to produce more heat

increase = will move to the endothermic reaction to reduce heat, reduces yield

Question 20

What happens when the temperature of a system at equilibrium is increases or decreases in an ENDOTHERMIC reaction?

and why

Answer 20

increasing temp = increase yield as the equilibrium will move in the exothermic direction to produce less heat

decreasing = decreases yield, move to the exothermic direction to produce more heat.

Question 21

What happens when pressure increases or decreases in an equilibrium reaction

Answer 21

• an increase in pressure causes the equilibrium position to shift towards the side with the smaller number of molecules
• a decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules

Question 22

What happens when concentration increases or decreases in an equilibrium reaction

Answer 22

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 23

What are the three methods of measuring the rate of reaction for gases?

Answer 23

Using an inverted measuring cylinder

Using a gas syringe

Allow the reaction to proceed in an open container placed on an electronic balance. The gas is allowed to escape and the consequent mass loss can be measured against time over the course of the reaction.

Question 24

What are the different ways to measure the rate of reactions

Answer 24

• if reaction forms precipitate: the time taken for a fixed amount of precipitate (product) that causes a cross to disappear can be measured. This is proportional to the initial rate of reaction.
• measure time taken for colour change, change in pH or temperature

Question 25

Describe the collision theory

Answer 25

For two particles to react, they must collide at the correct orientation and have sufficient energy.