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Chemistry - Word Equations (AQA Syllabus A)
Sugar → carbon dioxide + ethanol. This is the word equation for fermentation, the process by which beer and wine are made.

Chemistry - Word Equations (AQA Syllabus A)

It is necessary for students of GCSE Science to have a basic grasp of the fundamental ideas in chemistry. This is the fifth of six quizzes recapping those ideas and it looks specifically at word equations - the method of writing down chemical reactions in words rather than in symbols.

When chemicals react together new chemicals are made from the original ones present. One of the best ways of describing what happens in the reaction is to write a chemical equation. When writing a chemical equation you can use two methods - using symbols to represent the chemicals or by using words. A chemical equation tells you which chemicals reacted together (the reactants) and the new chemicals that were made in the reaction (the products). An example is the reaction of sodium with oxygen:

sodium + oxygen → sodium oxide.

Sodium and oxygen are the reactants and there is just one product, sodium oxide.

Unfortunately, even just writing the words 'chemical equation' send shivers down the spines of many students who see them as really complicated to do and there are so many to learn as well, aren't there? Actually, no, you don't need to learn many, but how come?

In most cases, for reactions involving metals, there are fairly simple rules that you can follow. For example, if you know that metal carbonates react with strong acids to form the metal salt, water and carbon dioxide, and you know which salt comes from which acid, you are able to write a word equation for the reaction of any metal with the acids that you know about - that's around 300 word equations from a couple of simple pieces of information. If you haven't realised that, then chemical equations are going to be tough for you because you will have to learn them all individually! You will only be asked to write them for reactions you have come across during your studies.

For reactions between non-metals (including hydrocarbon fuels burning), it is a bit more complex. For example, the reaction of sulfur with oxygen:

sulfur + oxygen → sulfur dioxide.

You would need to know the product is sulfur dioxide and not sulfur oxide - but if you think about it, it is always sulfur dioxide that you will have heard of during your study of science.

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1.
What type of reaction is illustrated by the following word equation?

methane + oxygen → carbon monoxide + water
Incomplete combustion
Complete combustion
Incomplete reduction
Complete polymerisation
This word equation represents what happens when any hydrocarbon fuel is burnt in a limited amount of air
2.
Which of the following is the correct word equation for the reaction between magnesium carbonate and an acid?
magnesium carbonate + sulfuric acid → magnesium sulfite + water + carbon dioxide
magnesium carbonate + nitric acid → magnesium nitrate + water + carbon dioxide
magnesium carbonate + hydrochloric acid → magnesium chloride + water
magnesium carbonate + nitric acid → magnesium nitrate + hydrogen + carbon dioxide
When answering questions like this, make sure you check that you have the correct salt for the acid as well as the correct other products from the reaction
3.
When a reactive metal reacts with water, it forms the metal hydroxide and hydrogen. Which of the following is the correct word equation for a Group 1 metal?
calcium + water → calcium hydroxide + hydrogen
aluminium + water → aluminium hydroxide + hydrogen
lithium + water → lithium hydroxide + hydrogen
magnesium + steam → magnesium hydroxide + hydrogen
The others are not in Group 1 of the periodic table
4.
Where a metal reacts directly with a non-metal, the name of the resulting chemical ends in which letters?
-ide
-ate
-ite
-ic
Chemical names ending in -ate or -ite always contain oxygen as well as the other non-metal. So if you wrote the word equation carbon + sulphur → carbon sulfate, you should realise that it is wrong because there is no oxygen on the side of the reactants
5.
What elements are present in the reactants in the following chemical reaction?

Magnesium carbonate + hydrochloric acid → magnesium chloride, water and carbon dioxide?
Mg, C, H, Cl
Mg, C, O, Zn, Cl
Mg, C, O, H, Cl
Mg, Na, H, S, O
You should be able to get this from the names but if you are not sure, you can also check by looking at the products
6.
Which of the following lists gives the salts that are made from the common lab acids - sulfuric, nitric and hydrochloric?
Sulfite, nitrite, chlorate
Sulfite, nitrate, chlorate
Sulfate, nitrate, chlorate
Sulfate, nitrate, chloride
There are chemical reasons for these names but for your exam you just need to remember which acid forms which salt
7.
Which of the following word equations shows the thermal decomposition of limestone?
calcium oxide → calcium + oxygen
calcium hydroxide → calcium + water
calcium carbonate → calcium hydroxide + carbon dioxide
calcium carbonate → calcium oxide + carbon dioxide
For the exam, you should know that the main chemical of limestone is calcium carbonate and when metal carbonates undergo thermal decomposition they form the metal oxide and release carbon dioxide
8.
Which of the following is the correct word equation for the reaction of a metal with an acid?
copper + sulfuric acid → copper sulfite + hydrogen
zinc + hydrochloric acid → zinc nitrate + oxygen
sodium + nitric acid → sodium nitrate + oxygen
magnesium + sulfuric acid → magnesium sulfate + hydrogen
Metals above hydrogen in the reactivity series will react with strong acids to form the metal salt and hydrogen. Options 2 and 3 can be discarded immediately as they break the law of conservation of matter. The wrong salt is mentioned in the first option - you get sulfates from sulfuric acid
9.
What sort of reaction is represented by the following word equation?

iron oxide + carbon monoxide → iron + carbon dioxide?
Thermal decomposition
Reduction
Oxidation
Catalytic cracking
This is one of the reactions taking place in the blast furnace to produce iron
10.
What is the missing chemical in the word equation:

sugar → carbon dioxide + _______
Methane
Ethane
Methanol
Ethanol
You should recognise this as being the word equation for fermentation

 

Author:  Kev Woodward

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