C5 Exothermic and Endothermic Reactions (page 138)

Question 1

Whenever chemical reaction occur, there are changes in energy, what do this mean?

Answer 1

This means that when chemicals get together, things either hot up or cool right off.

Question 2

Energy is moved around in what?

Answer 2

Chemical Reactions

Chemicals store a certain amount of energy - and different chemicals store different amounts.

Question 3

If the products of a reaction store more energy than the original reactants, what do this mean?

Answer 3

they must have taken in the difference in energy between the products and reactants from the surroundings during the reaction.

Question 4

If the products of a reaction store less, what do this mean?

Answer 4

the excess energy was transferred to the surroundings during the reaction.

Question 5

Why dont the overall amount of energy not change regarding the products of a reaction?

Answer 5

This is because energy is conserved in reactions - it can’t be created or destroyed, only moved around. This means the amound of energy in the universe always stays the same.

Question 6

What is Exothermic reaction?

Answer 6

it is one which transfers energy to the surroundings, usually by heating. This is shown by a rise in temperature

Question 7

What is the best example of an exothermic reaction?

Answer 7

burning furels - also called combustion. This gives out a lot of energy - it’s very exothermic.

Question 8

Are Neutralisation reactions (acid + alkali) exothermic?

Answer 8

yes

Question 9

Many oxidation reactions are exothermic, give an example?

Answer 9

adding sodium to water releases energy, so it must be exothermic (see page 108). The reaction releases energy and the sodium moves about on the surface of the water as if it is oxidised.

Question 10

Exothermic reactions have lots of everyday uses, give some examples?

Answer 10

Some hand warmers use the exothermic oxidation of iron in air (with a salt solutuion catalyst) to release energy.

Self heating cans of hot chocolate and coffee also rely on exothermic reactions between chemicals in their bases

Question 11

In an Exothermic reaction is heat given out or taken in?

Answer 11

Given out

Question 12

In an Endothermic Reaction is heat given out, or is heat taken in?

Answer 12

Taken in

Question 13

What is Endothermic reaction?

Answer 13

is one which takes in energy from the surroundings. This is shown by a fall in temperature

Endothermic reactions are much less common than exothermic reactions, but the include:

Thermal decomposition - e.g. heating calcium carbonate causes it to decompose into calcium oxide (also called quicklime and carbon dioxide:

Calcium carbonate - CaCO3 (+ HEAT) &raquo_space;»> CO2 + CaO - Quicklime

Question 14

What everyday uses do Endorthermic reaction have?

Answer 14

Endorthermic reactions are used in some sports injury packs - the chemical reaction allows the pack to become instanly cooler withoug having to put it in the freezer

Question 15

What is an easy way to remember the difference between Exothermic and Endothermic reactions?

Answer 15

Exo = exit “-thermic” = heat, so an exothermic reacton is one that gives out heat

and endothermic means just the opposite.

Question 16

A student prepares a flask containing ethanoic acid and measures its temperature as 22.5°C. She then adds dilute potassium hydroxide solution which is 21°C, After 2 minutes the temperature of the reaction mixture is 28.5°C. Is the reaction exothermic or endothermic? (1 mark)

Answer 16

Exothermic (1 mark)