C5 Monitoring and Controlling Chemical Reactions

(Total RFM of desired products / Total RFM of all products) X100

Better for profits and environment

(Actual Yield / Predicted Yield) X100

Evaporation, Filtration, Reversible Reactions, Transfer of Liquid.

The mass of pure, dry product. It depends on the amount of reactants you started with Calculated by: weighing the dried product

The maximum possible mass of pure product that could be produced using the reactants you started with Calculated from: the balanced symbol equation by using the maths of measuring the mass in reaction

This is the actual yield of the product expressed as a percentage of the theoretical yield

Percentage yield = Actual yield (grams) / Theoretical yield (grams) x 100

100%. This is because some product is always lost along the way - e.g through purification and drying

Rust

Chemical weathering, like acid rain damage to limestone buildings

Magnesium reacting with acid, producing a gentle stream of bubbles

Burning is fast, but explosions are even faster and release a lot of gas

• Safety - If the reaction is too fast it could cause a dangerous explosion • Economic reasons - Changing conditions can be costly. E.G using high temperatures means there are larger fuel bills, increasing cost of production. Companies often have to choose optimum conditions that give low production costs, but this may mean compromising on the rate of production or yield

Increase in temperature Increase in concentration Catalyst added Solid reactant crushed up into smaller bits (surface area)

Particles move faster More collisions take place Particles have more kinetic energy, meaning they have enough energy required for making the collision successful

More particles within the same volume, therefore increasing chances of a collision

Surface area is increased Particles have more area to work on

A substance that speeds up the reaction without being changed or used up in the reaction Gives reacting particles a surface to stick to where they can bump into, increasing the number of successful collisions

Amount of reactant used or amount of product formed Time

• Precipitation and colour change • Change in mass (usually gas given off) • Volume of gas given off

When the product of the reaction is coloured, or is a precipitate that clouds the solution Precipitate: Measure the time it takes for a mark through the solution to disappear. The faster it disappears, the faster the reaction. This only works if the initial solution was see-through Colour change: If reactants are coloured and products are coloured (or vice versa), you can time how long it takes for the solution to lose (or gain) a colour. Results are subjective however, people may not agree with eachother on an exact point this occurs

Measuring the speed of a reaction that produces a gass, by using a mass balance The change in mass as the gas is given off can be seen on the balance. The quicker the reading drops the faster the reaction. Rate of reaction graphs are easy to plot using this method and is the most accurate method, but has the disadvantage of releasing the gas straight into the room

Involves a gas syringe to measure the gas given off The more gas given off during a given time interval, the faster the reaction. Gas syringes are accurate to the nearest cm^3, so are quite accurate. Although too vigorous of a reaction can blow the plunger out of the syringe, which is costly