Topic 7

Question 1

What is the rate of reaction?

Answer 1

The rate of reaction is how quickly a reaction happens.

Question 2

How can the rate of reaction be observed?

Answer 2

It can be observed either by measuring how quickly the reactants are used up or how quickly the products are formed.

Question 3

How can the rate of reaction be calculated ?

Answer 3

Rate of reaction = amount of reactant used or amount of product formed/ time

Question 4

What does the rate of chemical reaction depend on (process)?

Answer 4

1) The collision frequency of reacting particles (how often they collide). The more successful collisions there are, the faster the reaction is.
2 )The energy transferred during collisions. The minimum energy that particle’s need to react when they collide is called the activation energy. Particles need to collide with at least the activation energy for the collision to be successful.

Question 5

How does a reaction occur?

Answer 5

Reactions happen if the particles collide with enough energy to react

Question 6

What happens if you increase the number of collisions?

Answer 6

So if you increase the number of collisions or the energy with which the particles collide, the reaction happens more quickly (i.e. the rate increases).

Question 7

What are the three factors that affect the rate of reaction?

Answer 7

1) Temperature
2) Concentration
3) Surface Area

Question 8

What happens when you increase the temperature?

Answer 8

Increasing the Temperature increase the rate:

1) When the temperature is increased the particles move faster. If they move faster, they’re going to have more collisions.
2) Higher temperatures also increase the energy of the collisions, since the particles are moving faster. Reactions only happen if the particles collide with enough energy.
3) This means that at higher temperatures there will be more successful collisions (more particles will collide with enough energy to react). So increasing the temperature increases the rate of reaction.

Question 9

What happens when you increase the concentration?

Answer 9

Increasing the concentration/ pressure increase the rate:

1) If a solution is made more concentrated it means there are more particles of reactant in the same volume. This makes collisions more likely, so the reaction rate increases.
2) In a gas, increasing the pressure means that the particles are more crowded. This means that the frequency of collisions between particles will increase- so the rate of reaction will also increase.

Question 10

What happens when you increase the surface area?

Answer 10

Smaller solid particles/ more surface are means a higher rate:

1) If one reactant is a solid, breaking it into smaller pieces will increase its surface area to volume ratio (i.e. more of the solid will be exposed compared to its overall volume).
2) The particles around it will have more area to work on, so the frequency of collisions will increase.
3) This means that the rate of reaction is faster for solids with a larger surface area to volume ratio.

Question 11

What is the equation for the gradient?

Answer 11

gradient= change in y/ change in x

Question 12

What is a catalyst?

Answer 12

1)A catalyst is a substance which increases the rate of a reaction, without being chemically changed or used up in the reaction.

Question 13

Will the catalyst affect the reaction?

Answer 13

1)Using a catalyst won’t change the products of the reaction- so the reaction will stay the same.

Question 14

Does the catalyst need to be used in big amounts?

Answer 14

1) Because it isn’t used up, you only need a tiny bit to catalyse large amounts of reactants

Question 15

How do catalyst affect the rate of reaction? (process)

Answer 15

1) Catalysts work by decreasing the activation energy needed for a reaction to occur.
2) They do this by providing an alternative reaction pathway that has lower activation energy.
3) As a result, more of the particles have at least the minimum amount of energy needed for a reaction to occur when the particles collide

Question 16

What are enzymes?

Answer 16

1)Enzymes are biological catalysts

Question 17

What do enzymes do?

Answer 17

1) They catalyse (speed up) the chemical reactions in living cells.

Question 18

Examples of reactions that have been catalysed by enzymes : (prp)

Answer 18

1) Photosynthesis
2) Respiration
3) Protein synthesis

Question 19

What does the change of temperature depend on?

Answer 19

1) The change in temperature depends on the reagents used- You can measure the temperature change for different types of reaction

Question 20

Dissolving salts in water (process– change of temperature):

Answer 20

1) You can measure the temperature change when dissolving salts in water by adding the salt to a polystyrene cup of water and measuring the change on temperature when the salt has dissolved
2) Dissolving ammonium chloride decreases the temperature of the temperature of the reaction mixture –it’s endothermic.
3) Dissolving calcium chloride causes the temperature of the solution to rise- it’s exothermic

Question 21

Neutralisation Reactions( process– change of temperature):

Answer 21

1) In a neutralisation reaction, an acid and a base react to form a salt and water. Most neutralisation reactions are exothermic.
2) However, the neutralisation reaction between ethanoic acid and sodium carbonate is endothermic

Question 22

Displacement (process– change of temperature):

Answer 22

1) In a displacement reaction, a more reactive element displaces a less reactive element in a compound. These types of reactions are accompanied by a release of energy- they’re exothermic.
2) Zinc powder and copper sulphate react in a displacement reaction forming zinc sulphate and copper

Question 23

Precipitation Reactions (process– change of temperature):

Answer 23

1) Precipitates are insoluble solids which can sometimes form when two solutions are mixed together.
2) Precipitation reactions are exothermic. For example the reaction between lead (II) nitrate solution and potassium iodide forming a lead iodide precipitate would result in an increase on the temperature of the surroundings.

Question 24

What is an exothermic reaction?

Answer 24

An exothermic reaction is one which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature of the surroundings

Question 25

What happens on an exothermic reaction graph?

Answer 25

1) The products are at a lower energy than the reactants,

2) The difference in height represents the energy given out in the reaction

Question 26

What is an endothermic reaction?

Answer 26

An endothermic reaction is one which takes in energy form the surroundings, usually on the form of heat and usually shown by a fall in temperature of the surroundings.

Question 27

What happens on an endothermic reaction graph?

Answer 27

1) The products are at a higher energy than the reactants.

2) The difference in height represents the energy taken in during the reaction

Question 28

What happens during a chemical reaction?

Answer 28

1) During a chemical reaction, old bonds are broken and new bonds are formed.

Question 29

Is the chemical reaction endothermic or exothermic?

Answer 29

1) Energy must be supplied to break existing bonds- so bond breaking is an endothermic process.
2) Energy is released when new bonds are formed- so bond formation is an exothermic process.

Question 30

What happens to the energy in an endothermic reaction?

Answer 30

1)In endothermic reactions, the energy used to break bonds is greater than the energy released by forming them.

Question 31

What happens to the energy in an exothermic reaction?

Answer 31

1) In exothermic reactions, the energy released by forming bonds is greater than the energy used to break them.

Question 32

What is the overall heat energy change for an exothermic reaction?

Answer 32

1)Exothermic if more heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants

Question 33

What is the overall heat energy change for an endothermic reaction?

Answer 33

1) Endothermic if less heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants.

Question 34

What does every chemical reaction have?

Answer 34

1) Every chemical bond has a particular bond energy associated with it. This bond energy varies slightly depending on the compound the bond occurs in.

Question 35

How do you calculate the overall energy change?

Answer 35

Overall energy change= energy required-energy formed

Question 36

What does a positive energy change mean?

Answer 36

A positive energy change means an endothermic reaction .

Question 37

What does a negative energy change mean?

Answer 37

A negative energy change means an exothermic reaction.

Question 38

What is the activation energy?

Answer 38

1)The activation energy is the minimum amount of energy needed for bonds to break and a reaction to start.

Question 39

What is the activation energy on a reaction profile?

Answer 39

1)On a reaction profile, it’s the energy difference between the reactants and the highest point of the curve.

Question 40

What happens if the energy input is less than the activation energy?

Answer 40

1)If the energy input is less than the activation energy there won’t be enough energy to start the reaction- so nothing happens.

Question 41

What are sodium thiosulfate and hydrochloric acid?

Answer 41

There are both clear, colourless solutions, which react together to form a yellow precipitate of sulfur.

Question 42

Sodium thiosulfate and hydrochloric acid )practical):

Answer 42

1) Measure out fixed volumes of sodium thiosulfate and hydrochloric acid, using a measuring cylinder.
2) use a water bath to gently heat both solutions to the desired temperature before you mix them.
3) Mix the solutions in a conical flask. Place the flask over a black mark on a piece of paper which can be seen through the cloudy , yellow sulfur and time how long it takes.

• The reaction can be repeated for solutions at different temperatures.
• The depth and volume of liquid must be kept the same each time.
• The concentration of the solutions must be kept the same.
• The shorter the length of time taken for the mark to disappear, the faster the rate.