Chemistry Unit 2: Calculations etc.

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What is an exothermic reaction?
An exothermic reaction transfers heat to its surroundings e.g. combustion, oxidation and neutralisation. They can be used in hand warmers and self heating coffee.
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What is an endothermic reaction?
An endothermic reaction transfers energy from its surroundings e.g. thermal decomposition. They can be used for self cooling injury packs.
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What is a reversible reaction?
A reversible reaction means the products can go back and form the reactants, e.g hydrated copper sulphate anhydrated copper sulphate + water
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What is meant by an isotope?
Isotopes are elements containing the same amount of protons but a different number of neutrons
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What is the Relative Atomic Mass (Ar)?
The average value of the masses of the isotopes, every Ar is compared with 12^C
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What is the Relative Formula Mass (Mr)?
The Mr tells us the mass of a compound, to calculate the Mr we multiply the mass number of the element by how many atoms of the element there is in the compound e.g CH4 Mr = (1x12)+(4x1) = 16
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How do you calculate the percentage of an element in a compound?
To calculate the percentage of an element in a compound take the mass of the element and divide it by the relative formula mass then multiply it by 100 e.g % of carbon in CH4= 12/16 x100 = 75%
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How do you calculate the empirical formula?
Write the elements in separate columns and write the mass or percentage of each element underneath, divide each mass or percentage by the Ar of the element to get the ratio of the two elements
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How do you calculate the mass of a product given the mass of a reactant?
Work out the balanced equation, then work out the relative masses of each substance, and convert these masses into units, find the ratio of the two by dividing by the smallest value, then multiply the ratio of the unknown by the mass of the known
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What are the three reasons for a lower yield than expected?
One reason is some of the product could have been lost (e.g. filtration), there may have been side reactions taking place, the reaction may have been reversible
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How do you calculate the % yield?
You take the actual mass of the product and divide it by the expected mass of the product and multiply the answer by 100
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Other cards in this set

Card 2

Front

What is an endothermic reaction?

Back

An endothermic reaction transfers energy from its surroundings e.g. thermal decomposition. They can be used for self cooling injury packs.

Card 3

Front

What is a reversible reaction?

Back

Preview of the front of card 3

Card 4

Front

What is meant by an isotope?

Back

Preview of the front of card 4

Card 5

Front

What is the Relative Atomic Mass (Ar)?

Back

Preview of the front of card 5
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