Unit 6 - Chemical reactions

Doesn’t alter what the substance is, it only changes the appearance

When a chemical reaction changes what a substance is, so that the reactants are different from the products

The speed at which a reaction takes place

1.At the beginning the gradient is steep because many reactant particles are present so the rate is fast 2.The gradient starts to decrease - one of the reactant particles starts to get used up (limiting reagent) 3.At the end there are no more reactant particles so the reaction stops and the line plateaus

Rate = Volume of gas (cm^3) ÷ time (s)

Rate = mass loss (g) ÷ time (s)

• Concentration - More particles gives an increased chance of successful collisions • Pressure - more particles in a smaller volume causes more collisions • Surface area - reaction takes place on surfaces, hence more surface increases the rate of reaction - can be done by decreasing particle size • Temperature - increased temperature leads to particles gaining more energy and moving faster, hence more collisions • Use of a catalyst - speed up rates of reactions by lowering activation energy

• Particles must collide • Particles must collide with correct orientation (head-on) • Particles must collide with sufficient kinetic energy

Directly proportional

When the rate of the forward reaction is equal to the rate of reverse action and at this point there is no change in the proportion of reactants or products

• Rate of the forwards reaction equals the rate of backward reaction • The concentrations of reactants and products remain constant 3, Reaction occurs in a closed system - no exchange of substances with the surroundings

• If reactant concentration increases equilibrium shifts to remove the extra reactant by increasing the yield of product • If product concentration increases equilibrium shifts to remove extra product by decreasing yield of product

• If pressure is increased equilibrium shifts to the side with fewer moles to reduce overall pressure • If pressure is decreased equilibrium shifts to the side with more moles to increase overall pressure

When a change is made on a reversible reaction at chemical equilibrium, then the equilibrium moves in the direction that will oppose that change and bring the system back to equilibrium

• Temperature increase leads to equilibrium shift to the endothermic reaction to counteract temperature increase by having less product form • Temperature decrease leads to equilibrium shifting to exothermic to result in a higher yield of products

• Simultaneous • Oxidation - gain of oxygen or loss of electrons or increase in oxidation number • Reduction - loss of oxygen or gain of electrons or decrease in oxidation number

• When oxidation state becomes more positive, oxidation is occurring • When oxidation state becomes less positive, reduction is occurring

A substance that oxidizes another substance during a redox reaction

A substance that reduces another substance during a redox reaction