Every reaction breaks bonds and makes bonds. Whether it releases or absorbs energy depends on which costs more.
An exothermic reaction releases energy to the surroundings: the temperature rises and ΔH is negative (combustion, neutralisation). An endothermic reaction absorbs energy: the temperature falls and ΔH is positive (thermal decomposition, photosynthesis).
Add up the bond energies for bonds broken and bonds made. In a calorimetry experiment the energy transferred to water is q = m × c × ΔT, where c for water is 4.2 J/g/°C.
A reaction in which the temperature of the surroundings rises is:
ΔH for an endothermic reaction is:
Breaking bonds is always:
Which process is endothermic?
H₂ + Cl₂ → 2HCl. Bonds broken: H–H 436 and Cl–Cl 243 kJ.
What is the total energy to break the bonds, in kJ?
Enter an exact answer, without rounding.Making 2 H–Cl bonds of 432 kJ each releases energy.
What is the energy released, in kJ?
Enter an exact answer, without rounding.Broken 679 kJ and made 864 kJ.
What is ΔH, in kJ/mol?
Enter an exact answer, without rounding.100 g of water is heated by 5 °C (c = 4.2 J/g/°C).
How much energy is transferred, in J?
Enter an exact answer, without rounding.Which equation gives the energy in calorimetry?
ΔH = bonds broken − bonds made. A negative result means:
Which is an exothermic change?
A reaction energy profile for an exothermic reaction shows products:
The specific heat capacity of water is:
Petroleum comes out of the ground as thick black liquid. Separating it gives the fuel for planes, the tar for roads and the raw material for plastics.
The fossil fuels are coal, natural gas and petroleum. The main part of natural gas is methane. Petroleum is a mixture of hydrocarbons, which are compounds of hydrogen and carbon only.
Petroleum is separated into fractions in a fractionating column, which is hot at the bottom and cooler at the top. Going up the column, the fractions have shorter chains, higher volatility, lower boiling points and lower viscosity.
A hydrocarbon contains:
The main constituent of natural gas is:
Petroleum is separated into fractions by:
Going up the fractionating column, the chain length:
Bitumen is used for:
Kerosene is mainly used as:
Octane has the formula C₈H₁₈.
How many atoms are in one molecule?
Enter an exact answer, without rounding.A column separates petroleum into refinery gas, gasoline, naphtha, kerosene, diesel oil, fuel oil, lubricating oil and bitumen.
How many fractions is that?
Enter an exact answer, without rounding.Which is a fossil fuel?
Compared with bitumen, petrol has a:
The fractionating column is hottest:
The naphtha fraction is mainly used as a:
Volatility describes how easily a liquid:
How you get a metal out of the ground depends on how reactive it is. Iron needs a furnace taller than a house, and aluminium needs a huge electric current.
Metals low in the reactivity series are easy to obtain. Iron is extracted from hematite in the blast furnace. Coke burns to give heat, and carbon monoxide then reduces the iron(III) oxide. Limestone removes impurities as slag.
Aluminium is more reactive than carbon, so it is extracted by electrolysis. Its main ore is bauxite. Purified aluminium oxide is dissolved in molten cryolite, which lowers the operating temperature and saves energy.
The main ore of iron used in the blast furnace is:
In the blast furnace, the main reducing agent is:
Limestone is added to the blast furnace to:
Aluminium is extracted by electrolysis because it is:
Cryolite is used because it:
Carbon anodes must be replaced because they:
Fe₂O₃ + 3CO → 2Fe + 3CO₂
How many moles of iron form from 1 mole of Fe₂O₃?
Enter an exact answer, without rounding.Fe₂O₃ has a relative formula mass of 160 (Fe = 56).
What mass of iron, in g, comes from 160 g of Fe₂O₃?
Enter an exact answer, without rounding.The main ore of aluminium is:
Burning coke in the blast furnace mainly provides:
Slag has the chemical formula:
At the cathode in aluminium extraction:
Metals that are low in the reactivity series are:
About half the world’s food relies on nitrogen fertiliser, which is made from air by one reversible reaction.
Ammonia is made by the Haber process: N₂(g) + 3H₂(g) ⇌ 2NH₃(g). Nitrogen comes from air and hydrogen comes from methane.
The Contact process is a step in making sulfuric acid: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). Sulfur dioxide comes from burning sulfur or roasting sulfide ores, and oxygen comes from air.
Ammonium salts and nitrates are used as fertilisers. NPK fertilisers supply nitrogen, phosphorus and potassium for better plant growth.
In the Haber process, the hydrogen comes from:
The catalyst in the Haber process is:
The catalyst in the Contact process is:
High pressure favours ammonia in the Haber process because:
In NPK fertiliser, K stands for:
N₂ + 3H₂ ⇌ 2NH₃
How many moles of NH₃ could form from 6 moles of H₂?
Enter an exact answer, without rounding.The Haber process runs at 20 000 kPa and the Contact process at 200 kPa.
How many times greater is the Haber pressure?
Enter an exact answer, without rounding.A 25 kg bag of fertiliser is 40% nitrogen.
What mass of nitrogen does it hold, in kg?
Enter an exact answer, without rounding.The symbol ⇌ shows that a reaction is:
The Contact process typically runs at:
The Contact process converts:
A catalyst in a reversible reaction:
Which compound is used as a fertiliser?
Clean water and clean air are chemistry problems. You can test for them, treat them and work out where pollution comes from.
Test for water with anhydrous copper(II) sulfate (white to blue) or anhydrous cobalt(II) chloride (blue to pink). Pure water boils at exactly 100 °C and melts at exactly 0 °C. Natural water can hold useful substances (dissolved oxygen, some minerals) and harmful ones (toxic metals, plastics, sewage, microbes, nitrates and phosphates).
Clean, dry air is about 78% nitrogen and 21% oxygen, with the rest mainly noble gases and carbon dioxide.
For climate change: plant trees, reduce livestock farming, burn less fossil fuel and use more hydrogen and renewable energy. For acid rain: use catalytic converters, low-sulfur fuels and flue gas desulfurisation with calcium oxide.
Anhydrous copper(II) sulfate turns in water from:
Pure water can be identified by its:
In water treatment, chlorine is added to:
Carbon is used in water treatment to remove:
Carbon monoxide comes from:
Which gas is a main cause of acid rain?
Clean air is about 78% nitrogen.
How many litres of nitrogen are in 500 litres of air?
Enter an exact answer, without rounding.Clean air is about 21% oxygen.
How many litres of oxygen are in 200 litres of air?
Enter an exact answer, without rounding.Nitrates and phosphates in rivers cause:
Methane in the air comes partly from:
Catalytic converters help to reduce:
Flue gas desulfurisation uses:
Which helps to reduce climate change?
Chemists work like detectives. A colour, a fizz or a flame is the clue that tells you what is in an unknown sample.
A flame test identifies some metal ions by colour. Each common gas also has its own test.
Add aqueous sodium hydroxide, then aqueous ammonia. Note the colour of any precipitate and whether it dissolves in excess.
Each anion has its own test. For the silver nitrate and barium nitrate tests, add dilute nitric acid first to remove carbonate, which would also form a precipitate.
A compound gives a lilac flame. It contains:
A yellow flame test shows the presence of:
A glowing splint relights in:
Damp red litmus paper turning blue shows:
NaOH(aq) gives a red-brown precipitate with:
A light blue precipitate forms with NaOH(aq) and stays in excess. The ion is:
Dilute nitric acid and aqueous silver nitrate give a yellow precipitate with:
A white precipitate with acid and aqueous barium nitrate shows:
Limewater turning milky shows:
A lighted splint gives a squeaky pop with:
Which two ions both give white precipitates with NaOH(aq) that dissolve in excess?
Damp litmus paper is bleached by:
A carbonate is identified by adding dilute acid and testing the gas with:
The oxide of an element tells you whether it behaves as a metal or a non-metal. A fuel cell runs a car and leaves only water behind.
Metal oxides are usually basic and non-metal oxides are usually acidic. Amphoteric oxides react with both acids and bases to form a salt and water.
A hydrogen–oxygen fuel cell uses hydrogen and oxygen to produce electricity, with water as the only chemical product.
Calcium oxide is:
Sulfur dioxide is:
Which oxide is amphoteric?
An amphoteric oxide reacts with:
The only chemical product of a hydrogen–oxygen fuel cell is:
A disadvantage of hydrogen fuel cells is that hydrogen:
2H₂ + O₂ → 2H₂O
How many moles of water form from 4 moles of hydrogen?
Enter an exact answer, without rounding.CuO + 2HCl → CuCl₂ + H₂O
How many moles of HCl react with 3 moles of CuO?
Enter an exact answer, without rounding.Non-metal oxides are usually:
Which pair are both amphoteric?
Copper(II) oxide reacts with hydrochloric acid to form:
Compared with a petrol engine, a fuel cell in use produces:
A fuel cell produces:
Questions from every topic in this course. Pick an answer for each one, then hit Check My Answers.
50 g of water rises by 10 °C. The energy absorbed (c = 4.2) is:
An exothermic reaction:
Which reaction is endothermic?
ΔH for an exothermic reaction is:
Breaking chemical bonds is:
On an energy profile diagram, the activation energy is:
Breaking bonds takes in 1,000 kJ and making bonds releases 1,200 kJ. ΔH is:
A thermometer in a reaction mixture rises from 20 °C to 32 °C. The reaction is:
Which fraction is used as fuel for cars?
Petroleum is:
In the blast furnace, iron(III) oxide is:
What is dissolved in molten cryolite?
The Haber process makes:
NPK fertilisers supply:
The first stage of domestic water treatment removes:
Oxides of nitrogen mainly come from:
A blue-green flame shows the presence of:
The test for a chloride uses dilute nitric acid and:
Which oxide reacts with an acid but not with a base?
A hydrogen–oxygen fuel cell needs: