GCSE Chemistry- C6 Chemical changes

observations for a chemical reaction

colour change, change in temperature, effervescence, solid/precipitate formed

rate of reaction

how fast reactants are used up and how fast products are made

Methods to determine rate of reaction

mass loss- loss of mass in reactants over time (weighed before vs after with balance), gas collection- volume of gas formed over time (gas syringe), precipitation- formation of a precipitate over time

Mean rate of reaction

quantity of reactant used/time taken or quantity of product formed/time taken

uncertainty

range in which the true value should lie

uncertainty equation

±range/2

mole

1 mol is the amount of substance that contains the same number of particles as there are atoms in 12.0g of carbon12

Measuring moles

no direct way of measuring moles- calculated using mass or volume then divided over time

higher concentration of reacting solutions

increase ROR, as there are more particles in the same volume- meaning collisions are more frequent

higher pressure of reacting gases

increases ROR as there are the same number of particles in less volume, or there are more particles in the same volume

higher surface area of solid reactants

increases ROR as there is a greater surface area to volume ratio (SA:V)- meaning more collisions can occur more frequently

higher temperature

increases ROR as particles have more kinetic energy and move faster- meaning collisions are more frequent with enough energy to overcome the activation energy

Catalysts

increases ROR by providing an alternative reaction pathway with a lower activation energy

collision theory

chemical reactions can only occur when reacting particles collide with each other with sufficient energy

activation energy

the minimum amount of energy that particles must have to react

reaction to completion

the reactants are used up to form the product molecules and the reaction stops when all of the reactants are used up

reversible reactions

product molecules can react themselves with each other or decompose and form the reactant molecules again

reversible reaction theory

Forward reaction (forms products): A+B→ C+D

Reverse reaction (forms reactants): C+D→ A+B

written as A+B⇌C+D

Dynamic equlibrium

rate of the forward reaction is the same as the rate of the reverse reaction

chemical reaction

when a new substance is made

effect of concentration on ROR RP reaction

sodium thiosulphate + hydrochloric acid → sodium chloride + sulfur dioxide + sulfur

Na₂S₂O₃ (aq) + 2HCl (aq) → NaCl (aq) + H₂O (l) + SO₂ (aq) + S (s)

variables in effect of concentration on ROR RP

independent variable- sodium thiosulphate concentration

dependent variable- time taken for cross to disappear (ROR)

control: Volume of HCl, concentration of HCl

Le chatlier’s principle

if a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change

Sodium hydroxide used to identify some metal ions (cations)

solutions of Al, Ca and Mg ions form white precipitate when sodium hydroxide solution is added, but only the aluminium hydroxide solution precipitate dissolves in excess sodium hydroxide solution from displacement, Na is more reactive than Al

Solutions of Copper (II), Iron (II) and Iron (III) used for identification

Cu (II) forms blue precipitate when sodium hydroxide solution added

Fe (II) forms green precipitate when sodium hydroxide solution added

Fe (III) forms brown precipitate when sodium hydroxide solution added

Carbonate identification reaction

reacts with dilute acids to form carbon dioxide gas- CO₂ can be identified with limewater-forms cloudy/milky solution through precipitates

Halide identification reaction

produces precipitates with silver nitrate solution in presence of dilute nitric acid- doesn’t displace

silver chloride- white precipitate formed

silver bromide- cream precipitate formed

silver iodide- yellow precipitate formed

sulphates identification

produces a white precipitate with barium chloride solution in presence of dilute HCl

Photon

particle of light with a set wave length

Wavelengths of metal compounds

Lithium- crimson colour

Sodium- yellow-orange colour

Copper- blue-green colour

potassium- lilac

instrumental methods

elements and compounds can be detected and identified using instrumental methods using a machine

advantages of instrumental methods

accurate, sensitive, rapid

Flame emission spectroscopy

an example of an instrumental method used to analyse metal ions in solution

Flame emission spectroscopy process

sample put in flame and light given out is passed through a spectroscope, output is aline spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations