c5 rates of reactions

Question 1

how can the rate of a chemical reaction be measured?

Answer 1

quantity of product (or reactant used) // time taken

Question 2

what is the rate of a chemical reaction?

Answer 2

how fast the reactants are changed into products

Question 3

what are some examples of slow reactions?

Answer 3

1) iron rusting
2) chemical weathering, eg acid rain damage to limestone buildings

Question 4

what is an example of a moderate speed reaction?

Answer 4

magnesium reacting with an acid to produce a gentle stream of bubbles

Question 5

what are examples of fast reactions?

Answer 5

1) burning
2) explosions

Question 6

what does the steepness of a line in rate of reaction graph represent?

Answer 6

the rate of the reaction

Question 7

what do flat lines show in a rate of reaction graph represent?

Answer 7

they show that the reaction has finished

Question 8

how can you find the rate of a reaction between two points?

Answer 8

work out the overall change in y (which is the product formed) divided by change in x (which is the time taken)

Question 9

how can you find the rate of a reaction at a particular point?

Answer 9

1) draw a tangent that touches the curve at one point but doesnt cross it.
2) find the gradient of that tangent by picking 2 points which are easy to read and calculate the gradient of that tangent ( using change in y // change in x)

Question 10

what are some of the factors that affect the rate of a reaction?

Answer 10

• temperature
• pressure (of gas)
• concentration (of solution)
• catalyst
• surface area

Question 11

what does the collision theory state?

Answer 11

1) the rate of reaction is dependent on:
- the collision frequency of the reaction. the more collisions there are, the faster the reaction is.
- the energy transferred during a collision. particles have to collide with enough energy for the collision to be successful

Question 12

how does increasing the temperature in a reaction affect the rate of a reaction?

Answer 12

• INCREASES RATE-
  1) when the temperature increases, the particles have more kinetic energy, which means they move faster.
  2) if they’re moving faster, they’re going to collide more frequently.
  3) furthermore, if they have more energy, then more of the collisions will have enough energy to make the reaction happen

Question 13

how does increasing the concentration or pressure affect the rate of reaction?

Answer 13

• INCREASES RATE-
  1) if the solution is made more concentrated, it means that there are more particles knocking about in the same volume of the solvent.
  2) similarly, when the pressure of gas is increased, it means that the same number of particles occupies a smaller space.
  3) this all makes collisions between the reactant particles more frequent.

Question 14

how to increase pressure?

Answer 14

make the container containing the gas smaller

Question 15

how does increasing the surface area affect the rate of reaction?

Answer 15

• INCREASES RATE-
  1) if one of the reactants are a solid, breaking it up will increase its surface area to volume ratio.
  2) this means that for the same volume of the solid, the particles around it will have more area to work on- so there will be collisions more frequently

Question 16

how does using a catalyst increase the rate of a reaction?

Answer 16

• INCREASES RATE-
  1) a catalyst is a substance that increases the rate of a reaction, without being used up itself, therefore it is not part of the reaction equation.
  2) they all work by decreasing the activation energy needed for the reaction to occur.
  3) they do this by providing an alternative reaction pathway with a lower activation energy.

Question 17

what is a reversible reaction?

Answer 17

a reaction where the products can react with one another to create the reactants again

Question 18

what happens during equilibrium?

Answer 18

both reactions are still happening but there is no overall effect (its a dynamic equilibrium) . this means that the concentrations of reactants and products are balanced and WONT change

Question 19

when can equilibrium be reached?

Answer 19

if the reversible reaction takes place in a ‘closed system’, so no reactants or products can escape

Question 20

what is the conc balance from reactants to products if the equilibrium lies to the right?

Answer 20

the concentration of the products is higher than the reactants

Question 21

what is the conc balance from the reactants to the products if the equilibrium lies to the left?

Answer 21

the concentration of the reactants is higher than the products

Question 22

what conditions does the position of equilibrium depend on?

Answer 22

• temperature
• concentration
• pressure (for gasses)

Question 23

what is the rule on endothermic and exothermic reactions in reversible reactions?

Answer 23

if the reaction is endothermic in one direction, it’ll be exothermic in the other

Question 24

what is the energy transferred FROM the surrounding by the endothermic reaction equal to?

Answer 24

the energy transferred TO the surroundings during the exothermic reaction

Question 25

what is an example of a reversible decomposition reaction?

Answer 25

1) hydrated copper sulfate into anhydrous copper sulfate + water

• if u heat blue hydrated copper sulfate crystals, it dries the water off and leaves anhydrous white copper sulfate powder. (ENDOTHERMIC)
• but if u add water back, it turns the white powder back into the blue crystals. (EXOTHERMIC)

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 can Le Chatelier’s principle be used to predict?

Answer 27

the effect of any changes you make to a reaction system

Question 28

what happens when you change the temperature at equilibrium?

Answer 28

DECREASE TEMP:
1) equilibrium would move to the exothermic reaction to produce more heat.
2) this means that you’ll get more products for the exothermic reaction and fewer products for the endothermic reaction.
INCREASE TEMP:
1) the equilibrium will shift to the endothermic reaction to try and decrease it.
2) you’ll now get more products for the endothermic reaction and fewer products for the exothermic reaction.

Question 29

```what happens when you change the pressure of a gas at equilibrium?