C6 revision

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Rate of chemical reactions

Activation energy:
The sufficient amount of energy particles need to cause a reaction.
Rate of reaction is dependent on the number of successful collisions.

At low concentrations, there will be fewer collisions because there are fewer particles there to collide with each other.
At high concentrations, it is more likely there will be successful collisions as there are more particles, therefore the particles collide more frequently.

Low temperatures mean there is less energy, therefore the particles move slower and do not have enough energy to break bonds.
High temperatures mean more energy, therefore there will be more successsful collisions.

If the surface area of the particles is increased there will be more collisions and a faster rate of reaction because more of the substance is exposed.

Adding a catalyst allows the reaction to occur at a faster rate. Catalysts reduce the amount of energy needed for the reaction.

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Endothermic and exothermic reactions

Exothermic:
Give out energy to surroundings.

Endothermic:
Energy is taken in form surroundings.

If the substance in a test tube was having an endothermic reaction, the test tube would feel cold to touch.

If a substance in a test tube was having an endothermic reaction, it would feel hot to touch.

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Chemical synthesis

Chemical synthesis:
The process of raw materials being made into useful products.

E.g.
Food additives
Fertilisers
Paints
Dyes
Pigments
Pharmaceuticals

Bulk chemicals are made on a large scale. Fine chemicals are made on a small scale.

Top three range of chemical made in industry and laboratories in UK:
Pharmaceuticals 31.5%
Soaps, toiletries and cleaning preparations 11.5%
Other specialities 13%

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Hazard symbols

Flammable:
A flame on a straight line.

Corrosive:
Two test tubes pouring drops onto a damaged hand and object.

Explosive:
A circle with broken rock and debris shooting from it.

Oxidising:
A circle with flames coming from the top.

Harmful:
A giant X.

Toxic:
A skull and crossbones.

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Acids and alkalis

pH scale:
Measures alkalinity or acidity of an aqueous solution on a 14 point scale.
14--------------------------------------7-------------------------------------1
Alkali Neutral Acid
Purple Green Red

Detect using litmus paper.
Measure by using a universal indicator or a pH meter.

Acidic compounds produce aqueous hydrogen ions H+(aq) when they dissolve in water. Alkali compounds produce aqueous hydroxide ions OH-(aq) when they dissolve in water. If it ends in hydroxide - it's an alkali.

Remember:
Nitric acid HNO3
Sulphuric acid H2SO4
Hydrogen chloride HCl
Sodium hydroxide NaOH
Magnesium hydroxide Mg(OH)2

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Neutralisation reactions

Acids react with alkalis to form salts.

Acid + alkali -> salt + water

E.g.
Hydrochloric acid + sodium hydroxide -> sodium hydroxide + water

HCl + NaOH -> NaCl + H2O

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Calculating theoretical yield

1. Work out relative formula masses.
2. Divide the formula mass of unknown compound by the known compound.
3. Multiply the answer by the amount of known chemical

E.g.
How much calcium oxide is theoretically possible to make from 1kg of calcium carbonate?

1. CaCO3 CaO
Ca = 40 Ca = 40
C = 12 O= 16
O = 16 + 16 + 16 Add them up=
Add them up = 56
100

2. Known compound = CaCO3. 56/100 = 0.56

3. 0.56 * 1kg = 0.56 kg of CaO produced

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Calculating actual yield of chemicals (quantity)

1. Work out relative formula masses.
2. Divide RFM of unknown chemical by RFM of known chemical.
3. Multiply answer by known quantity.

E.g. What mass of sodium hydroxide is needed to produce 1 tonne of sodium sulphate.

2NaOH + H2SO4 -> Na2SO4 + 2H2O
Sodium hydroxide + sulphuric acid -> sodium sulphate + water

1. NaOH = 40 (but because there is 2NaOH its 40*2 =80) and NaSO4 = 142

2. 80/142 =0.56

3. 0.56 * 1 tonne = 0.56 tonnes of sodium hydroxide is needed to produce 1 tonne of sodium sulphate.

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