Rates of Reactions

Question 1

What is reaction rate?

Answer 1

How fast a reaction happens

Question 2

How is reaction rate observed?

Answer 2

Measuring how quickly reactants are turned into products or how quickly they are used up

Question 3

Formula for rate of reaction

Answer 3

Amount of reactant used or amount of product formed / time

Question 4

Benefits of fast reactions in industry

Answer 4

Making the required product as cheaply as possible maximises profit
Yield more product in a given time

Question 5

Drawbacks of fast reactions in industry

Answer 5

Expensive to generate conditions

Safety concerns

Question 6

What does the collision theory explain?

Answer 6

Why reactions occur at different rates and how they occur

Question 7

What does the collision theory state must happen for chemical reactions to occur?

Answer 7

Particles must collide with enough energy (the activation energy)

Question 8

What does the rate of a chemical reaction depend on?

Answer 8

Frequency of collisions between reacting particles

Amount of energy transferred in a collision

Question 9

What does increasing the rate of reaction mean increasing?

Answer 9

The number of collisions and / or energy of reacting particles

Question 10

How can we increase the rate of reaction?

Answer 10

Increase temperature
Increase concentration/ pressure in gases
Increase surface area to volume ratio

Question 11

How can we calculate reaction rates from a graph?

Answer 11

Draw tangent and work out it’s gradient

Question 12

What does a smaller gradient tell us?

Answer 12

Slower rate of reaction

Question 13

How can we observe how concentration affects reaction rate? What is seen?

Answer 13

Precipitation reaction

A colour change

Question 14

What solutions must we use for a precipitation reaction?

Answer 14

2 see through solutions that mix to form a precipitate which clouds the solution

Question 15

What are 2 solutions we could use in a precipitation reaction?

Answer 15

Sodium thiosulfate and hydrochloric acid

Question 16

How is a precipitation reaction carried out?

Answer 16

Put a conical flask on top of a sheet of paper with an X in the centre
Pour in solution that is not acid
Pour in acid with a known concentration and press start on stop watch
Stop when you can’t see X

Question 17

What should we repeat precipitation reactions with?

Answer 17

Different acid concentrations

Question 18

What are the independent and dependent variables for precipitation reactions?

Answer 18

Acid concentration

Time taken for cross to disappear

Question 19

How can reaction rate be measured with a mass change?

Answer 19

A gas is released and lost mass is measured on a mass balance

Question 20

What shows a faster reaction in a mass change experiment?

Answer 20

Quicker the reading on the mass balance drops

Question 21

How do we show surface area affecting reaction rate?

Answer 21

Hydrochloric acid and marble chips

Question 22

Experiment to show surface area affecting reaction rate

Answer 22

Place a known mass of marble chips in a measuring cylinder and pour in an excess volume of acid with a known concentration
Record volume of gas given off every second using a gas syringe

Question 23

What are the independent and dependent variables in the surface area experiment?

Answer 23

Surface area of the marble chips

Volume of gas given off each second

Question 24

When had the marble chip reaction finished?

Answer 24

When no more gas is produced

Question 25

How should the surface area experiment be repeated?

Answer 25

Same volume and concentration of acid and the same mass of marble chips but with more crunched up (increased surface area) Then repeat with powdered chalk

Question 26

What chemicals are used to measure how temperature affects reaction rate?

Answer 26

Sodium thiosulfate | Hydrochloric acid

Question 27

What do sodium thiosulfate and hydrochloric acid react to form?

Answer 27

Yellow precipitate of sulfur

Question 28

In the experiment to measure how temperature affects reaction rate, what is the measure of this reaction?

Answer 28

The time taken for the precipitate to form

Question 29

Steps for temperature experiment

Answer 29

Measure out fixed volumes of sodium thiosulfate and hydrochloric acid using a measuring cylinder and heat in a water bath to a desired temperature Mix in a conical flask and place on white paper with a cross on it Time how long it takes for black cross to disappear

Question 30

How should the experiment to measure temperature affecting reaction rate be changed?

Answer 30

Different temperatures

Question 31

Why does increasing temperature increase reaction rate?

Answer 31

Increases collision frequency | Makes reactants gain energy so a greater proportion will have more energy than activation energy needed

Question 32

Why does increasing concentration/ pressure increase rate of reactions?

Answer 32

Higher collision frequency | More particles of the same reactant in the same volume

Question 33

What do catalysts do?

Answer 33

Increase reaction rates

Question 34

Why are catalysts used in industrial reactions?

Answer 34

Reduce energy costs

Question 35

Why are catalysts efficient?

Answer 35

Aren’t chemically changed or used up in reactions | Small amount needed to catalyse large amounts of reactants

Question 36

What will catalysts not change?

Answer 36

Products

Question 37

Why do catalysts increase the likelihood of collisions?

Answer 37

Decrease activation energy needed for a reaction to occur

Question 38

How do catalysts decrease activation energy?

Answer 38

Provide an alternative reaction pathway that has a lower activation energy

Question 39

What show a reaction’s progress?

Answer 39

Reaction profiles

Question 40

What happen during chemical reactions?

Answer 40

Energy changes

Question 41

What does an increase / decrease in temperature depend on?

Answer 41

Which reagents are used in the reaction

Question 42

What reactions cause changes in heat energy?

Answer 42

Salts dissolving in water Neutralisation - most exothermic Displacement - most exothermic Precipitation - exothermic

Question 43

Experiment to measure temperature change when dissolving salts in water

Answer 43

Add salt to polystyrene cup of water and measure temperature change when salt has dissolved

Question 44

Exothermic reactions

Answer 44

Energy from reacting chemicals transferred to surroundings leading to temperature increase

Question 45

Examples of exothermic reactions

Answer 45

Combustion Neutralisation Oxidation Hand warmers

Question 46

Endothermic reactions

Answer 46

Energy from surroundings transferred to reacting chemicals, decreasing temperature of the surroundings

Question 47

Examples of endothermic reactions

Answer 47

Sports injury packs Thermal decomposition Citric acid + baking soda

Question 48

What must be supplied to break bonds? What type of reaction is this?

Answer 48

Energy | Endothermic

Question 49

What happens to bonds during a chemical reaction?

Answer 49

Old bonds are broken and new bonds are formed

Question 50

What is released when new bonds are formed? What type of reaction is this?

Answer 50

Energy | Exothermic

Question 51

Bond energy calculations

Answer 51

Overall energy = energy required to break bonds - energy released by forming bonds

Question 52

What is overall energy change measured in?

Answer 52

KJ mol-1

Question 53

Experiment to measure change in temperature of a reaction

Answer 53

Polystyrene cup into large beaker of cotton wood Add known volume of reagent to cup and measure initial temperature of the solution Add measured mass of second reagent and stir Put a lid on cup Record max/ min temperature that it reaches Calculate temperature change

Question 54

Why is a polystyrene cup used? What does it reduce?

Answer 54

Good thermal insulator | How much the external temperature affects the reaction

Question 55

Why is cotton wool used? What does it reduce?

Answer 55

Gives insulation | Energy transfer to or from reaction mixture