Chemistry - 8 Rates and Equilibrium - 8.4 The Effect of Concentration and Pressure & 8.5 The Effect of Catalysts & 8.6 Reversible Reactions

The effect of concentration on rate of reaction [3]:

- as concentration increases, there are more particles in the same volume
- particles collide more frequently
- the rate of reaction increases

The effect of (gas) pressure on rate of reaction [3]:

- as pressure increases, there are more particles in a given space
- particles collide more frequently
- the rate of reaction increases

Marble chemical formula

CaCO₃ (calcium carbonate)

CaCO₃ + HCl →

CaCl₂ + CO₂ + H₂O

Catalyst

substance that speeds up the rate of a chemical reaction but is unchanged itself

The effect of catalysts on rate of reaction [3]:

- catalyst provides an alternative reaction pathway requiring less activation energy
- more particles have the required activation energy
- there are more successful collisions
- the rate of reaction increases

Advantages of catalysts [4]:

- less energy required
- lower temperatures and pressures
- conserves fossil fuels
- less expensive

A catalyst cannot be used indefinitely because...

it becomes 'poisoned' by reaction with impurities

Reversible reaction

a chemical reaction in which the products reform the original reactants

Reversible reaction symbol

⇌

Difference between reactions in a reversible reaction

one is endothermic while the other is exothermic

How to change the direction of a reversible reaction

change conditions so equilibrium shifts

Litmus alternative name

HLit

Litmus reversible reaction

HLit ⇌ H⁺ + Lit⁻

Litmus in acids

HLit (red)

Litmus in alkalis

H⁺ + Lit⁻ (blue)

Examples of reversible reactions [3];

- litmus paper
- salts and water of crystallisation
- ammonium chloride

Salts and water of crystallisation reversible reaction:

hydrated salt ⇌ anhydrous salt + water

Ammonium chloride reversible reaction:

NH₄Cl ⇌ NH₃ + HCl

Ammonium chloride forward reaction [2]

- thermal decomposition
- products become gases

Ammonium chloride backward reaction [2]

- gases cool and react
- form solid