Topic 7- Rates of reaction and energy changes

Question 1

Core Practical: Investigate the effects of changing the
conditions of a reaction on the rates of chemical reactions by:
a) measuring the production of a gas (in the reaction between
hydrochloric acid and marble chips)
b) observing a colour change (in the reaction between sodium
thiosulfate and hydrochloric acid)

Answer 1

a. Surface area: You could set up the apparatus , conical flask , gas syringe , stopwatch. Then measure the volume produced using gas syringe. Repeat the experiment with the same amount of volume and concentration of acid , with the exact same mass of marble chips , but more scrunched up .
b. Temprature : measure out fixed volume of sodium thiosulfate and hydrochloric acid. Use a water bath to heat up both solutions to desired temprature, before mixing them. Then place them in a conical flask and mix and place over a piece of paper with a cross. Watch and see how long it takes for the cross mot to be seen. Then try with diffrent tempratures . Keep concentration, volume the same.

Question 2

Suggest practical methods for determining the rate of a given
reaction

Answer 2

• measuring the volume of gas given off by a reaction over time.
• measuring the loss of mass of a reaction over time when a gas is produced.

Question 3

Explain the effects on rates of reaction of changes in
temperature, concentration, surface area to volume ratio of a
solid and pressure (on reactions involving gases) in terms of
frequency and/or energy of collisions between particles

Answer 3

Temperature : when temperature is increased the particles begin to move faster , so they have more chance of collision.
Concentration: if its more concentrated then there are more particles in the same volume , collisions are more likely to happen
Pressure; when you increase the pressure , means particles are more crowded , so frequency of collisions would increase.
Solid particles ;smaller with higher surface area , so higher surface area to volume ratio, so more of the solid is exposed

Question 4

How to calculate the rate of reaction from a graph

Answer 4

gradient= change in y divide change in x

Question 5

What is a catalyst?

Answer 5

Catalyst speeds up the rate of reaction without being used up itself and can be reused.

Question 6

Explain how the addition of a catalyst increases the rate of a
reaction in terms of activation energy

Answer 6

Catalyst decreases the activation energy needed for a reaction to occur , they do this by finding an alternative reaction pathway that has lower activation energy

Question 7

Recall that enzymes are biological catalysts and that enzymes
are used in the production of alcoholic drinks

Answer 7

Enzymes are a biological catalyst and they speed up the chemical reactions in living cells.

• enzymes from yeast cells are used in the fermentation process which is used to make alcoholic drinks
• they catalyse the reaction that coverts sugars into ethanol and carbon dioxide

Question 8

Recall that changes in heat energy accompany the following
changes:
a salts dissolving in water
b neutralisation reactions
c displacement reactions d
precipitation reactions
and that, when these reactions take place in solution,
temperature changes can be measured to reflect the heat
changes

Answer 8

a. dissolving salts in water - you can measure temperature change when dissolving salts in water by adding the salt to a polystyrene cup of water and measuring change in temperature once dissolved
b. neutralisation - mostly an acid and a base react to form salt and water (mostly exothermic)
c. displacement-more reactive one displaces a less reactive one- exothermic
d. precipitation- - insoluble solids which can sometimes form when two solutions are mixed together - exothermic

Question 9

Describe an exothermic change or reaction

Answer 9

Exothermic reaction gives out energy to the surroundings in a form of heat and is usually shown by a rise in temperature of surrounding

• in exothermic reactions the total energy of the products is less then the total energy of the reactants

Question 10

Describe an endothermic change or reaction

Answer 10

Endothermic reaction takes energy in from the surroundings in a form of heat and usually shown by a fall in temperature of the surroundings.

• In endothermic reactions the total energy of the products is higher then the total energy of the reactants

Question 11

Recall that the breaking of bonds and the making

of bonds

Answer 11

Bond breaking ;
- endothermic 
- takes energy in to break the bonds 
Bonds making;
-exothermic
- releases energy when new bonds form