25 KEY EQUATIONS

Avagadro’s number

6.02 × 10 to the power of 23

The mole

Moles = mass / relative atomic mass

Concentration

Concentration (mol/dm3) = moles / volume (dm3)

Cm and Dm

1dm3 is 1000cm3

Gas volumes 1

1 mol of any gas = 24dm3

Gas volumes 2

Volume (dm3) = moles x 24dm3

Percentage yield

Mass of product made / mass of what could’ve been made x 100 = percentage yield

Atom economy

Relative formula mass of desired product / Sum of relative formula mass of all reactants x 100 = atom economy

Energy changes

Energy change = Total energy to break bonds - total energy released making new ones (Break - make)

Rate of reactions

Mean rate of reaction = quantity of product formed / time taken

Chromatography

Rf = Distance moved by substance / distance moved by solvent

Combustion of carbon

Carbon + oxygen → Carbon dioxide

Combustion of hydrogen

Hydrogen + oxygen → Water

Combustion of hydrocarbons

Hydrocarbon + oxygen → carbon dioxide + water

Oxidisation of metals

Metal + oxygen → Metal oxide

Reaction of metals with water

Metal + water → Metal hydroxide + Hydrogen

Reactions of metals with acids

Metal + acid → salt + hydrogen

Reactions of metal oxides with acids

Metal oxide + acid → salt + water

Displacement of metals

Copper sulfate + magnesium → magnesium sulfate + copper

Ionic equation for displacement of metals

Cu2+ + Mg → Mg2+ + Cu

Neutralisation

Sodium hydroxide + acid → salt + water

Ionic equation for neutralisation

H+ + OH- → H2O

Marble chips (calcium carbonate) and acid

Calcium carbonate + acid → salt + water + carbon dioxide

Electrolysis of molten ionic compounds

Lead bromide → (molten) Lead + Bromine gas

Electrolysis of aqueous ionic compounds

Depends.

Negative cathode discharges the least reactive element

Positive anode discharges hydroxide ions unless there is a halogen present

Sodium chlorine + water → sodium hydroxide + hydrogen + chlorine

Half equations for electrolysis

Anode: 2Cl → Cl2 + 2e-

Cathode: 2H+ + 2e- → H2

Bromine test for alkenes

Ethene + Bromine → Dibromoethene

Bromine turns from orange to colourless.

The Haber process

Nitrogen + Hydrogen → Ammonia