Topic 7 - Rates of Reaction

Question 1

What is activation energy needed for?

Answer 1

During successful collisions, this energy helps to break bonds, so that the atoms can be rearranged in order to make new substances (the products of the reaction)

Question 2

When do chemical reactions occur?

Answer 2

When particles collide together with enough energy to break the original bonds.

Question 3

What is the rate of reaction?

Answer 3

The speed at which reactants are turned into products.

Question 4

What two ways can you measure the rate of reaction?

Answer 4

• By measuring how quickly a reactant disappears. By measuring how quickly a product is made

Question 5

How can we measure the rate of reaction in relation to the product?

Answer 5

We can find the rate of reaction by either measuring a mass produced in a given time (g/s) or a volume produced in a given time (cm³/s)

Question 6

What is the equation to calculate the mean rate of reaction by measuring the disappearance of the reactants?

Answer 6

Mean rate of reaction= quantity of reactants used/time taken (s)

Question 7

What is the equation to calculate the mean rate of reaction by measuring the appearance of the product?

Answer 7

Mean rate of reaction= quantity of product made/ time taken (s)

Question 8

How can we control the rate of reaction?

Answer 8

By altering variables such as the concentration of solution or the size of pieces of solid reactants.

Question 9

On a graph showing the rate of reaction, what does it mean if the line is steeper?

Answer 9

The steeper the line, the faster the rate of reaction.

Question 10

Why are reactant rates usually fastest at the start?

Answer 10

Because that is when the concentration of reactants is at its highest, so there are more particles available that collide into each other, meaning more collisions happen.

Question 11

How does a graph for the rate of reaction look?

Answer 11

The concentration is on the y-axis and time taken on the x-axis.

Question 12

How does a line for the reactants on a graph for the rate of reaction look?

Answer 12

It’s a negative curve that starts at the top and curves towards the bottom. When it levels off, all the reactants have been used up.

Question 13

How does a line for the products on a graph for the rate of reaction look?

Answer 13

It’s a positive curve that starts at the bottom and curves towards the top. When it levels off, the reaction has stopped.

Question 14

Suggest 2 practical methods you could use to measure the rate of reaction.

Answer 14

Put some acid in a conical flask and add metal pieces to it. Add a bung and a gas syringe on the top to measure the volume of gas collected, so you follow the rate of reaction. Then, Put some acid in a beaker and a metal carbonate, placing cotton wool on the top to stop acid spray from escaping. Put the beaker on a balance and measure the decrease in mass as carbon dioxide escapes from the beaker to follow the rate of reaction.

Question 15

What factors affect the rate of reaction?

Answer 15

Surface area, concentration (the number of particles), temperature, pressure (only for gases)

Question 16

What is the rate of reaction linked to?

Answer 16

Collision theory

Question 17

What is activation energy?

Answer 17

The minimum amount of energy needed to start a chemical reaction.

Question 18

What happens in successful collisions between particles?

Answer 18

The activation energy helps to break the bonds, so that the atoms can be rearranged to form new substances (the products of the reaction).

Question 19

What are exothermic reactions?

Answer 19

Chemical reactions that releases energy into the surroundings.

Question 20

What are endothermic reactions?

Answer 20

Chemical reactions that take in energy from their surroundings to proceed.

Question 21

How does surface area affect the rate of reaction?

Answer 21

By increasing the surface area to volume ratio (by decreasing the size of solid pieces while keeping the total volume of solid the same), increases the rate of reaction. This is because there is more surface for the collisions to occur on, meaning more successful collisions are made.

Question 22

How does concentration affect the rate of reaction?

Answer 22

Increasing the concentration of the reactants increases the rate of reaction because there are more reacting particles in the same volume so more successful collisions are likely to occur.

Question 23

How does temperature affect the rate of reaction?

Answer 23

Increasing the temperature increases the rate of reaction because reactant particles have more energy and therefore collide into each other more often and have more energy to react when they collide.

Question 24

How does pressure affect the rate of reaction?

Answer 24

Increasing the pressure of gases increases the rate of reaction because the reactant particles are squeezed closer together so collisions occur more often.

Question 25

How can you work out the rate of reaction by drawing a tangent to a curve in a graph showing the rate of reaction?

Answer 25

You draw a straight line from the point that is given to you. Then you find the gradient by finding the x and y coordinates at the bottom and the top of the line and then using this equation: (Y₂ - Y₁)/ (X₂ - X₁)

Question 26

What are enzymes?

Answer 26

Large complex protein molecules that act as catalysts in biological reactions.

Question 27

What is a catalyst?

Answer 27

A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change or change in mass and doesn’t alter the products of the reaction. This means that less activation energy is needed.

Question 28

Explain the core practical for reaction rates by measuring volumes of gases.

Answer 28

Set up the apparatus, so that a conical flask contains marble chips in acid and has a delivery tube leading to a trough filled with water and a measuring cylinder in it upside down. Measure acid into conical flask. Add 5g of small marble chips to flask. Immediately stopper flask and start stop clock. Note the total volume of gas produced every 30 seconds until the reaction is over. Try the experiment again with 5g of larger marble chips

Question 29

Explain the core practical for reaction rates by observing a colour change.

Answer 29

1) Place some sodium thiosulfate into a conical flask. Measure out some acid into a test tube. Clamp the conical flask in place in a water bath at a certain temperature and place the test tube into the same water bath. Record the temperature of both. After 5 mins, remove the flask and place on a piece of white paper marked with a cross. Add the acid to the thiosulfate and start the stop clock. Stop the clock when the cross disappears. Note this time and take the final temperature of the mixture. Repeat at three or four other temperatures

Question 30

What is the core practical for reaction rates with measuring volumes of gas observing?

Answer 30

How surface area affects the rate of reaction.

Question 31

What is the core practical for reactions rates with watching a colour change observing?

Answer 31

How temperature affect the rate of reaction.

Question 32

How is platinum used in industry?

Answer 32

Platinum is a catalyst and is used in the manufacture of nitric acid to ammonia.

Question 33

How do catalysts help in industry?

Answer 33

They make industrial processes more profitable because they produce products more quickly and lower the activation energy, which reduces costs. They also don’t usually need to be replaced because they aren’t used up.

Question 34

What does a catalyst provide?

Answer 34

An alternate reaction route which requires less activation energy. However, since less energy is needed to start the reaction, more reaction molecules have energy to make successful collisions. This means the reaction is faster.

Question 35

What are the catalysts in catalytic converters and what do they do?

Answer 35

Platinum and palladium are the catalysts and their presence lowers the activation energy needed to convert harmful gases into harmless ones. The metals used are expensive but don’t need to be replaced as they aren’t used up.

Question 36

How do the catalysts have a large surface area in a catalytic converter?

Answer 36

The catalysts are spread in a thin layer over a honeycomb structure in a catalytic converter.

Question 37

Explain how enzymes work.

Answer 37

Each enzyme molecule has a part with a specific shape called the active site. The reactant molecules (substrates) fit the shape of the active site. So each enzyme only fits one substrate and only catalyses one specific reaction.

Question 38

What does it mean for enzymes to become denatured?

Answer 38

The shape of their active site changes so substrates can’t fit into them anymore and they can’t catalyse a biological reaction.

Question 39

How can an enzyme become denatured?

Answer 39

If the temperature or pH increases too much and changes the shape of the active site permanently.

Question 40

How are enzymes used in alcoholic drinks?

Answer 40

Alcoholic drinks are produced using and enzyme in yeast. This enzyme catalyses the reaction in which glucose is converted into ethanol (alcohol) and carbon dioxide.