C5 Monitoring and Controlling Chemical Reactions

Question 1

Atom Economy Equation

Answer 1

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

Question 2

100% Atom Economy

Answer 2

Better for profits and environment

Question 3

Percentage Yield Equation

Answer 3

(Actual Yield / Predicted Yield) X100

Question 4

Ways to lose Yield

Answer 4

Evaporation, Filtration, Reversible Reactions, Transfer of Liquid.

Question 5

What is actual yield?

Answer 5

The mass of pure, dry product. It depends on the amount of reactants you started with

Calculated by: weighing the dried product

Question 6

What is theoretical yield?

Answer 6

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

Question 7

What is percentage yield?

Answer 7

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

Question 8

What is the equation for percentage yield?

Answer 8

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

Question 9

What will the percentage yield always be less than?

Answer 9

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

Question 10

What is one of the slowest chemical reactions?

Answer 10

Rust

Question 11

What is an example of a slow chemical reaction?

Answer 11

Chemical weathering, like acid rain damage to limestone buildings

Question 12

What is an example of a moderate speed chemical reaction?

Answer 12

Magnesium reacting with acid, producing a gentle stream of bubbles

Question 13

What is an example of a fast speed chemical reaction?

Answer 13

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

Question 14

Why is controlling the rate of reaction important in industry?

Answer 14

1. Safety
   - If the reaction is too fast it could cause a dangerous explosion
2. 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

Question 15

What are the four factors that could lead to an increased rate of reaction?

Answer 15

Increase in temperature

Increase in concentration

Catalyst added

Solid reactant crushed up into smaller bits (surface area)

Question 16

How does increasing temperature increase the rate of reaction?

Answer 16

Particles move faster

More collisions take place

Particles have more kinetic energy, meaning they have enough energy required for making the collision successful

Question 17

How does increasing concentration increase the rate of reaction?

Answer 17

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

Question 18

How does increasing surface area by crushing solids down into smaller particles increase the rate of reaction?

Answer 18

Surface area is increased

Particles have more area to work on

Question 19

How does using a catalyst increase the rate of reaction?

Answer 19

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

Question 20

How can the rate of reaction be calculated with a formula?

Answer 20

Amount of reactant used or amount of product formed

Time

Question 21

What are the three methods of measuring the rates of reactions?

Answer 21

1. Precipitation and colour change
2. Change in mass (usually gas given off)
3. Volume of gas given off

Question 22

Describe how precipitation and colour change is used to measure the rate of a reaction

Answer 22

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

Question 23

Describe how change in mass is used to measure the rate of reaction

Answer 23

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

Question 24

Describe how the volume of gas given off is used to measure the rate of reaction

Answer 24

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