C2.5 + 6 Exothermic/Endothermic reactions + Acids, bases and salts

Question 1

How do chemical reactions interact with their surroundings?

Answer 1

They transfer energy to and from their surroundings.

Question 2

What is an exothermic reaction?

Answer 2

A reaction which transfers energy to its surroundings usually in the form of heat which is shown by a rise in temperature.

Question 3

What is an endothermic reaction?

Answer 3

A reaction which absorbs energy from its surroundings usually in the form of heat which is shown by a fall in temperature.

Question 4

Give 3 examples of exothermic reactions.

Answer 4

• Combustion reactions
• Neutralisation reactions
• Oxidisation reactions

Question 5

Give 2 uses of exothermic reactions.

Answer 5

• Hand warmers (they use the oxidisation of iron in the air)

- Self heating cans use chemicals in their bases reacting exothermically to produce heat

Question 6

Name one example of an endothermic reaction.

Answer 6

Thermal decomposition

Question 7

Name one use of an endothermic reaction.

Answer 7

• Ice packs, they take in heat from your skin and cool it down.

Question 8

What is the rule of a reversible reaction?

Answer 8

If it is exothermic in one direction, it is endothermic in the opposite direction.

Question 9

What does the (l) state symbol mean?

Answer 9

Liquid

Question 10

What does the (s) state symbol mean?

Answer 10

Solid

Question 11

What does the (g) state symbol mean?

Answer 11

Gas

Question 12

What does the (aq) state symbol mean?

Answer 12

Aqueous - dissolved in water (a solution)

Question 13

What is an acid?

Answer 13

A substance with a pH less than 7

Question 14

What type of ions do acids form in water?

Answer 14

H+ ions

Question 15

What is an base?

Answer 15

A substance with a pH more than 7

Question 16

What type of ions do alkalis form in water?

Answer 16

OH-

Question 17

What is an alkali?

Answer 17

A base that dissolves in water

Question 18

What is the word equation for neutralisation?

Answer 18

acid + base ===> water + salt

Question 19

What is the equation for neutralisation in terms of ions?

Answer 19

H+ (aq) + OH- (aq) ====> H20 (l)

Question 20

What is the word equation for an acid and metal reaction?

Answer 20

acid + metal ===> salt + hydrogen

Question 21

What are three ways soluble salts can be made from acids?

Answer 21

• Reacting them with metals (not all are suitable, some are too reactive, others not reactive enough)
• Reacting them with insoluble bases (the base is added to the acid until no more reacts and the excess solid is filtered off)
• Reacting them with alkalis (an indicator is used to show when the acid and alkali have completely neutralised and reacted to produce a salt solution)

Question 22

How can salt solutions form solid salts?

Answer 22

By crystallization

Question 23

What does the reactivity of a metal have to do with how fast it reacts with an acid?

Answer 23

• The higher the reactivity of a metal over hydrogen, the faster it will react with an acid.

Question 24

Why doesn’t copper react with acid?

Answer 24

It is less reactive than hydrogen.

Question 25

How is the speed of an acid’s reaction with metal shown?

Answer 25

By the rate that hydrogen bubbles are given off

Question 26

What is a precipitate?

Answer 26

An insoluble salt that is formed when two ion solutions are reacted

Question 27

What can precipitation be used for?

Answer 27

Removing unwanted ions from solutions e.g treating water

Question 28

What are two examples of bases?

Answer 28

• Metal oxides

- Metal hydroxides

Question 29

What is the equation for acid and metal oxide/hydroxide?

Answer 29

acid + metal oxide/hydroxide ===> water + salt

Question 30

What does ammonia do when it dissolves in water?

Answer 30

It produces an alkali solution

Question 31

What is the word equation for ammonia reacting with nitric acid?

Answer 31

ammonia + nitric acid ====> ammonium nitrate

Question 32

What is ammonium nitrate useful for?

Answer 32

As a fertiliser, it has nitrogen from two sources (the nitric acid and ammonia), plants need nitrogen.

Question 33

Explain how to make a salt using potassium hydroxide and hydrochloric acid.

Answer 33

potassium hydroxide + hydrochloric acid ===> potassium chloride + water

• Add the potassium hydroxide to the hydrochloric acid, but only enough so that the acid is neutralised.
• Use a universal indicator (turning green) to tell when this is
• Put the solution in an evaporating dish and boil off half the water, then leave the precipitate to cool and crystallize in a warm place.

Question 34

Explain how to make a salt using copper oxide and sulphuric acid.

Answer 34

copper oxide + sulphuric acid ===> copper sulphate + water

• Add the copper oxide powder to the acid and let it dissolve.
• Eventually the solution cannot dissolve any more power as the reaction is complete. The excess copper oxide just floats in the solution.
• The excess powder is separated from the solution by pouring it through filter paper.
• The filtrate is then collected in evaporating dish, and only half boiled off.
• The rest is left to dry and crystallize over time