The Rate and Extent of Chemical Change

Question 1

what is the rate of chemical reaction?

Answer 1

how fast the reactants are changed into products

Question 2

what is collision theory?

Answer 2

the collision frequency of particles which transfers energy - the more collisions the faster the reaction is

Question 3

what is the minimum amount of energy needed to start a reaction?

Answer 3

activation energy

Question 4

why is activation energy needed?

Answer 4

to break the bonds in the reactants that start the reaction

Question 5

what 4 things does rate of reaction depend on?

Answer 5

temperature, concentration of a solution/pressure of a gas, surface area and the presence of a catalyst

Question 6

how does increasing the temperature increase the rate of reaction?

Answer 6

when the temperature is increased the particles will move faster meaning they will collide more frequently with more energy

Question 7

how does increasing concentration/pressure increase rate of reaction?

Answer 7

if a solution is more concentrated it means there are more particles knocking about in the same volume or in a smaller space making collisions more frequent

Question 8

how does increasing the surface area increase rate of reaction?

Answer 8

if one of the reactants is a solid then breaking it up into smaller pieces will increase the surface area to volume ratio meaning that the particles around the solid will have more area to work with so there will be more frequent collisions

Question 9

how does using a catalyst increase rate of reaction?

Answer 9

they decrease activation energy by providing a different reaction pathway with a lower activation energy

Question 10

how do you calculate rate of reaction?

Answer 10

amount of reactant used up or amount of product formed [divided by] time

Question 11

how can you measure rate of reaction using precipitation and colour change?What experiment could you use this in?

Answer 11

observe a mark through the solution and measure how long it takes to disappear/how long a solution takes to lose or gain colour
sodium thiosulphate and hydrochloric acid produce cloudy precipitation

Question 12

how can you measure rate of reaction using change in mass?

Answer 12

as a gas is released, the mass decreases - quicker decrease means faster rate

Question 13

how can you measure rate of reaction using the volume of gas given off?What experiment could you use this for?

Answer 13

the more gas given off the quicker the reaction

magnesium and hydrochloric acid to produce hydrogen gas

Question 14

what happens during a reversible reaction?

Answer 14

as the reactants react their concentrations fall so the forward reaction slows down but as more products are made and the concentration rises the backward reaction will speed up

Question 15

when is a reversible reaction at equilibrium?

Answer 15

when the forward reaction is going at exactly the same rate as the backward one

Question 16

what is happening to the reaction at equilibrium?

Answer 16

both reactions are still happening but there is no overall effect meaning the concentrations of the reactants and products have reached balance and wont change

Question 17

what has to happen for equilibrium to be reached?

Answer 17

the system has to be closed

Question 18

what is a closed system?

Answer 18

none of the reactants or products can escape and nothing can get in

Question 19

what does it mean if the equilibrium lies to the right?

Answer 19

the concentration of products is greater than that of the reactants

Question 20

what does it mean if the equilibrium lies to the left?

Answer 20

the concentration of reactants is greater than that of the products

Question 21

what does the position of the equilibrium depend on?

Answer 21

the temperature, the pressure, the concentration of the reactants and products

Question 22

what happens if the reversible reaction is endothermic in one direction?

Answer 22

it will be exothermic in the other and vice versa

Question 23

what is the energy transferred from the surroundings during an endothermic reaction equal to?

Answer 23

the energy transferred to the surroundings during an exothermic reaction

Question 24

what happens if you heat blue hydrated copper sulphate crystals?

Answer 24

it drives the water off and leaves white anhydrous copper sulphate powder

Question 25

what happens if you then add drops of water to the white powder?

Answer 25

you get the blue crystals back again

Question 26

what is le chatelier’s principle?

Answer 26

the idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change

Question 27

what happens to the equilibrium if you decrease the temperature?

Answer 27

it will move in the exothermic direction to produce more heat meaning you will get more products for the exothermic reaction and fewer products for the endothermic reaction

Question 28

what happens to the equilibrium if you increase the temperature?

Answer 28

it will move in the endothermic direction to try and decrease it so you will get more products for the endothermic and fewer for the exothermic reaction

Question 29

what happens to the equilibrium if you increase the pressure?

Answer 29

the equilibrium tries to reduce it by moving in the direction where there are fewer molecules of gas

Question 30

what happens to the equilibrium if you decrease the pressure?

Answer 30

the equilibrium tries to increase it by moving in the direction where there are more molecules of gas

Question 31

what happens to the equilibrium if you change the concentration of either of the reactants or products?

Answer 31

the system will no longer be at equilibrium so it responds to bring itself back to equilibrium

Question 32

what happens to the equilibrium when you increase the concentration of the reactants?

Answer 32

the system tries to decrease it by making more products

Question 33

what happens to the equilibrium if you decrease the concentration of products?

Answer 33

the system tries to increase it again by reducing the amount of reactants