Higher Chemistry | Unit 3 Part 1

Industrial processes are designed with what in mind?

To maximise profit and minimise impact on the environment.

Principles affecting industrial process design: (APOME)

- Availability, sustainability, and cost of feedstock

- Product yield

- Opportunity for recycling

- Marketability of by-products

- Energy requirements

Environmental considerations taken in industrial process design: (MADLS)

- Minimising waste and energy requirements

- Avoiding use or production of toxic substances

- Designing biodegradable products where appropriate

- Legislation and safety

Molar gas volume

- The volume occupied by one mole of any gas at a certain temperature and pressure.

- 1 mole of any gas at the same temperature and pressure will have the same volume, since most of the volume is made up of the spaces between particles.

- Spaces increase with increasing temperature and decreasing pressure

- n = V / Vm

Why are some reactions shaken with sodium hydroxide solution?

Sodium hydroxide solution absorbs carbon dioxide.

Controlling the rate of reaction

- If reaction rates are too low, the process is not economical.

- If reaction rates are too high, the process risks explosion.

Relative rate

- Relative rate is measured in s^1.

- 1/t

Collision theory

- Reactant particles must come into contact with each other for a reaction to take place.

- Not all collisions are successful due to incorrect orientation, so to increase success rate, you must increase the number of collisions that occur.

Activation energy

- The minimum energy required to initiate a chemical reaction.

- A low activation energy means a reaction will be fast and occur spontaneously at room temperature.

- A high activation energy means a reaction needs extra energy supplied to the reactant particles to ensure the energy of collision is greater than the activation energy.

Enthalpy change

- The difference between the enthalpy of the products and reactants.

- Exothermic reactions have a negative enthalpy change, as reactants have more energy than products. Energy is released to the surroundings.

- Endothermic reactions have a positive enthalpy change, as products have more energy than reactants. Energy is absorbed by the surroundings.

Activated complex

A high-energy, unstable, intermediate arrangement of atoms formed at the maximum of the potential energy barrier. This can go on to form products or fall back to form reactants.

Surface area on reaction rate

- Decreasing particle size increases surface area.

- Area of contact between particles increases.

- Number of collisions increases, so rate of successful collisions increases.

- Reaction rate increases.

Concentration on reaction rate

- Increasing concentration increases the number of reactant particles.

- Overall volume of reaction mixture remains the same.

- Spaces between reactant particles decrease.

- Number of collisions increases, so rate of successful collisions increases.

- Reaction rate increases.

Pressure on reaction rate

- Increasing pressure decreases volume of gas (compressed into a smaller space)

- Spaces between reactant particles decrease.

- Number of collisions increases, so rate of successful collisions increases.

- Reaction rate increases.

Temperature on reaction rate

- Increasing temperature increases the energy of each particle.

- Increased kinetic energy means particles move faster and are more likely to collide into one another.

- Number of collisions increases, so rate of successful collisions increases. Reaction rate increases.

- Increased kinetic energy means there are more particles with energy equal to or greater than the activation energy, meaning more particles can take part in the reaction.

- Number of collisions increases, so rate of successful collisions increases.

- Activation energy does not change.

Catalyst

A substance which speeds up chemical reactions without being consumed/used up.

- Provide an alternative reaction pathway with a lower activation energy, ie. lowers the activation energy of a reaction.

- No effect on enthalpy change.

Homogeneous catalyst

A catalyst in the same physical state as the reactants.

Heterogeneous catalyst

- A catalyst in a different physical state to the reactants.

- Gaseous or liquid reactions take place on the solid catalyst surface.

Catalyst poisoning

- When impurities present in reactants are absorbed onto catalyst surfaces, taking up “sites” for reactant particles.

- Surface area decreased, so surface activity also decreases as reactant particles cannot be absorbed. This renders a catalyst useless.

Solutions to catalyst poisoning:

- Renewal, where the spent catalyst is removed and replaced with a fresh one.

- Regeneration, where impurities are removed from active sites, usually by heating with a gas which reacts with the impurity.