C5 Monitoring and Controlling Chemical Reactions Flashcards
Atom Economy Equation
(Total RFM of desired products / Total RFM of all products) X100
100% Atom Economy
Better for profits and environment
Percentage Yield Equation
(Actual Yield / Predicted Yield) X100
Ways to lose Yield
Evaporation, Filtration, Reversible Reactions, Transfer of Liquid.
What is actual yield?
The mass of pure, dry product. It depends on the amount of reactants you started with
Calculated by: weighing the dried product
What is theoretical yield?
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
What is percentage yield?
This is the actual yield of the product expressed as a percentage of the theoretical yield
What is the equation for percentage yield?
Percentage yield = Actual yield (grams) / Theoretical yield (grams) x 100
What will the percentage yield always be less than?
100%. This is because some product is always lost along the way - e.g through purification and drying
What is one of the slowest chemical reactions?
Rust
What is an example of a slow chemical reaction?
Chemical weathering, like acid rain damage to limestone buildings
What is an example of a moderate speed chemical reaction?
Magnesium reacting with acid, producing a gentle stream of bubbles
What is an example of a fast speed chemical reaction?
Burning is fast, but explosions are even faster and release a lot of gas
Why is controlling the rate of reaction important in industry?
- 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
What are the four factors that could lead to an increased rate of reaction?
Increase in temperature
Increase in concentration
Catalyst added
Solid reactant crushed up into smaller bits (surface area)
How does increasing temperature increase the rate of reaction?
Particles move faster
More collisions take place
Particles have more kinetic energy, meaning they have enough energy required for making the collision successful
How does increasing concentration increase the rate of reaction?
More particles within the same volume, therefore increasing chances of a collision
How does increasing surface area by crushing solids down into smaller particles increase the rate of reaction?
Surface area is increased
Particles have more area to work on
How does using a catalyst increase the rate of reaction?
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
How can the rate of reaction be calculated with a formula?
Amount of reactant used or amount of product formed
Time
What are the three methods of measuring the rates of reactions?
- Precipitation and colour change
- Change in mass (usually gas given off)
- Volume of gas given off
Describe how precipitation and colour change is used to measure the rate of a reaction
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
Describe how change in mass is used to measure the rate of reaction
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
Describe how the volume of gas given off is used to measure the rate of reaction
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
