How do chemical reactions interact with their surroundings?
They transfer energy to and from their surroundings.
What is an exothermic reaction?
A reaction which transfers energy to its surroundings usually in the form of heat which is shown by a rise in temperature.
What is an endothermic reaction?
A reaction which absorbs energy from its surroundings usually in the form of heat which is shown by a fall in temperature.
Give 3 examples of exothermic reactions.
- Combustion reactions
- Neutralisation reactions
- Oxidisation reactions
Give 2 uses of exothermic reactions.
- Hand warmers (they use the oxidisation of iron in the air)
- Self heating cans use chemicals in their bases reacting exothermically to produce heat
Name one example of an endothermic reaction.
Thermal decomposition
Name one use of an endothermic reaction.
- Ice packs, they take in heat from your skin and cool it down.
What is the rule of a reversible reaction?
If it is exothermic in one direction, it is endothermic in the opposite direction.
What does the (l) state symbol mean?
Liquid
What does the (s) state symbol mean?
Solid
What does the (g) state symbol mean?
Gas
What does the (aq) state symbol mean?
Aqueous - dissolved in water (a solution)
What is an acid?
A substance with a pH less than 7
What type of ions do acids form in water?
H+ ions
What is an base?
A substance with a pH more than 7
What type of ions do alkalis form in water?
OH-
What is an alkali?
A base that dissolves in water
What is the word equation for neutralisation?
acid + base ===> water + salt
What is the equation for neutralisation in terms of ions?
H+ (aq) + OH- (aq) ====> H20 (l)
What is the word equation for an acid and metal reaction?
acid + metal ===> salt + hydrogen
What are three ways soluble salts can be made from acids?
- 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)
How can salt solutions form solid salts?
By crystallization
What does the reactivity of a metal have to do with how fast it reacts with an acid?
- The higher the reactivity of a metal over hydrogen, the faster it will react with an acid.
Why doesn’t copper react with acid?
It is less reactive than hydrogen.
How is the speed of an acid’s reaction with metal shown?
By the rate that hydrogen bubbles are given off
What is a precipitate?
An insoluble salt that is formed when two ion solutions are reacted
What can precipitation be used for?
Removing unwanted ions from solutions e.g treating water
What are two examples of bases?
- Metal oxides
- Metal hydroxides
What is the equation for acid and metal oxide/hydroxide?
acid + metal oxide/hydroxide ===> water + salt
What does ammonia do when it dissolves in water?
It produces an alkali solution
What is the word equation for ammonia reacting with nitric acid?
ammonia + nitric acid ====> ammonium nitrate
What is ammonium nitrate useful for?
As a fertiliser, it has nitrogen from two sources (the nitric acid and ammonia), plants need nitrogen.
Explain how to make a salt using potassium hydroxide and hydrochloric acid.
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.
Explain how to make a salt using copper oxide and sulphuric acid.
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
