Unit 4: Lesson 4: Catalysts Flashcards
What is a catalyst?
A catalyst is a substance that increases the rate of a reaction without being used up in the reaction. It remains chemically unchanged at the end of the reaction.
After the reaction, is the catalyst chemically changed or unchanged?
Chemically unchanged.
Ammonia is a key component of fertiliser. What catalyst is used to make the ammonia?
Iron oxide.
N2 + 3H2 –> NH3 (this is a reversible reaction as well).
What catalysts are used to make noxious gases from car exhausts inert?
Platinum and palladium.
What are enzymes?
Enzymes are catalysts produced by living things.
What type of catalyst is an enzyme?
A biological catalyst.
The Bombardier beetle sprays a hot liquid at predators. The liquid is the result of hydrogen peroxide splitting into water and oxygen. It produces a lot of heat. What biological catalyst catalyses this reaction?
Catalase, the enzyme.
2H2O2 (aq) –> 2H2O (l) + O2 (g)
What other catalysts break down hydrogen peroxide?
Manganese (IV) oxide and lead (IV) oxide.
Why don’t we write catalysts in equations?
Because they’re not chemically changed.
What do catalysts affect the rate of?
Catalysts affect the rate of a reaction.
What does it mean that a catalyst is specific?
They only catalyse certain reactions. Ensure you have the correct catalyst.
What types of reactions do catalysts provide an alternative route for?
Reactions which have a lower activation energy.
What does a lower activation energy mean regarding collisions?
A lower activation energy means more collisions are likely to be successful (result in product).
Can the original reaction still occur alongside the catalysed one?
Yes.
How can we use precipitation to demonstrate the effect of these (temperature, surface area/particle size, concentration/pressure and the presence of a catalyst) factors in different scenarios?
Place the conical flask containing the two solutions on a piece of paper with a cross. The time it takes to start to not see the cross indicates the rate of the reaction. This is very subjective (people may decide the cross is disappearing at different times) so is considered imprecise.
How can we use change in mass to demonstrate the effect of these (temperature, surface area/particle size, concentration/pressure and the presence of a catalyst) factors in different scenarios?
Many reactions produce gas. If we measure the mass of the reactants and then measure the mass lost over a set time, we find the rate of the reaction. The faster the mass decreases, the faster the reaction. Cotton wool is often placed in the opening of the flask to prevent anything but gas escaping.
How can we use the volume of gas given off to demonstrate the effect of these (temperature, surface area/particle size, concentration/pressure and the presence of a catalyst) factors in different scenarios?
This technique is similar to the previous, except the gas is collected and measured in a syringe. The more gas collected in a shorter time, the faster the rate of reaction. We know the reaction has finished when the volume of gas in the syringe doesn’t change. Be careful to use the correctly sized syringe. If too much gas is produced, the plunger could be forced off the syringe.
What practical (and apparatus) can we use to demonstrate how temperature effects the rate of a reaction?
Aapparatus:
- Sodium thiosulfate
- Hydrochloric acid
- Flask
- Paper
- Pen
Method:
1. Put hydrochloric acid and sodium thiosulfate into a flask.
2. Place flask onto paper with a cross drawn on.
3. Measure time for cross to obscure.
4. Change temperature and then repeat.
What practical (and apparatus) can we use to demonstrate how concentration effects the rate of a reaction?
Apparatus:
- Calcium carbonate marble chips
- Gas syringe
- Conical flask
- Hydrochloric acid
Method:
1. Place marble chips into a flask with hydrochloric acid.
2. Measure how much gas comes off at regular intervals of time.
3. Repeat with different concentrations of hydrochloric acid.
What practical (and apparatus) can we use to demonstrate how surface area/particle size effects the rate of a reaction?
Apparatus:
- Calcium carbonate marble chips
- Gas syringe
- Conical flask
- Hydrochloric acid
Method:
1. Place marble chips in a flask with hydrochloric acid.
2. Measure how much gas (CO2) comes off at regular intervals of time.
3. Repeat with different sized marble chips.
What practical (and apparatus) can we use to demonstrate how the presence of a catalyst effects the rate of a reaction?
Apparatus:
- Hydrogen peroxide (liquid)
- Conical flask
- Gas syringe
Method:
1. Place hydrogen peroxide into a conical flask.
2. Measure the volume of gas (O2) in the syringe after a set amount of time.
3. Repeat with 3 different solid catalysts (manganese oxide, zinc oxide and copper(II) oxide)
