Topic 5.

Question 0

Endothermic reaction.

Answer 0

Products are at a higher than the reactants.
On a graph-
The difference in height represents the energy taken in during the reaction.

Question 1

EXOTHERMIC reaction.

Answer 1

The products are at a lower energy than a reactant.
On a graph-
The difference in height represents the energy given out in a reaction.
The initial rise in the line represents the energy needed to break the old bonds.

Question 2

How would you measure the temperature changes in any of the reactions?

Answer 2

Dissolving salts in water.
Neutralisation reactions (where a solid and base react together).
Displacement reactions (where a more reactive element takes the place of a less reactive element.
Precipitation reaction (where two solutions react to produce an insoluble precipitate).

Question 3

How could you measure?

Answer 3

Measure the amount of energy produced by a chemical reaction in solution by taking the temperature of the reactions, mixing them in a cup and measuring the temp of the solution at the end.

Question 4

What is the problem with measuring temperature?

Answer 4

Is the amount of heat lost to the surroundings.

Question 5

How can you reduce it?

Answer 5

Putting the polystyrene cup into a beaker of cotton wool to give more insulation, and put a lid on it to reduce energy lost by evaporation.

Question 6

What’s an example?

Answer 6

Add dilute acid to a cup and measure the temp.
But a dilute solution into a measuring cylinder and record the temperature.
Make sure there the same temperature and add the alkali to the acid and stir.
Take the temp every 30 seconds until it reaches it’s peak temperature.

Question 7

What’s the slowest rate of reaction?

Answer 7

Rusting of iron.

Question 8

What’s a moderate reaction?

Answer 8

Metal reacting with acid to produce a stream of gentle bubbles.

Question 9

What’s a fast reaction?

Answer 9

Explosion.

Question 10

What does the rate of reaction depend on?

Answer 10

Temp
Concentration
Catalyst
Surface area

Question 11

Reaction of hydrochloric acid and marble chips.

Answer 11

Measure the volume of gas evolved with a gas syringe and take regular intervals.
Make a table of readings and plot a graph- time on the x axis and volume on the y axis.
Repeat with the same amount of acid and mass of marble chips but have the chips more crunched up (so there is a greater surface area).
Then repeat using powdered marble.

Question 12

What does this test?

Answer 12

The effect of an increasing surface area of a solid.

How the concentration of a acid affects the rate of a reaction.

Question 13

The effect of using finer particles.

Answer 13

Causes more collisions as there is a larger surface area.

If a greater mass the extra surface area gives a quicker reaction and more gas is evolved.

Question 14

Concentration.

Answer 14

A higher concentration gives a steeper graph.

Which causes the reaction to happen quicker.

Question 15

Sodium thiosulfate and hcl.

Answer 15

Produce a cloudy precipitate.
Both clear solutions.
They produce a precipitate of sulfur.
The excitement involves watching a black mark disappear through the cloudy sulfur and timing how long it takes.
Can be repeated using different temperatures.
The depth of the liquid must stay the same.
Results- the higher the temperature, the quicker the reaction- the less time it takes for the mark to disappear.

Question 16

What’s a catalyst?

Answer 16

Is a substance which changes the speed of a reaction, without being used up in the reaction.

Question 17

How does a catalyst work?

Answer 17

Works by lowering the energy required by the reactants to react.
Makes it easier for the reaction to happen and increase the rate of reaction.

Question 18

Catalyst converters

Answer 18

Found in motor vehicles.
Vehicle exhausts can give of poisonous gases if petrol doesn’t burn properly.
Used in the exhaust pipe.
Increases the rate that carbon monoxide and I brunt fuel reacts with oxygen in the air to produce carbon dioxide and water.
Catalyst has a large surface area and works best at a high temperature to increase the rate.

Question 19

Temperature.

Answer 19

The particles move quickly.

More frequent collisions.

Question 20

Concentration.

Answer 20

More particles of a reactant knocking between water molecules.
Collisions more likely.
In a gas increased pressure means particles are joe squashed up so there are more collisions.

Question 21

Surface area.

Answer 21

Breaking a solid into smaller pieces will increase the it’s surface area.
There will be a larger area to react with, so more frequent collisions.

Question 22

Catalysts

Answer 22

A solid catalyst works by giving the reacting particles a surface to stick to.
Increase the number of successful collisions by lowering the energy particles need to react with each other.

Question 23

Faster collisions increase the rate of reaction.

Answer 23

Faster collisions are only caused by increasing the temperature.
Reactions only happen if particles collide with enough energy.
Because minimal energy is needed to break initial bonds.
At a higher temp the are more particles colliding with enough energy.