Concentration, pressure, surface area, temperature and catalysts, plus both required practicals: the disappearing cross and measuring gas volume.
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1.Name the five factors that affect rate of reaction.
Concentration of solutions, pressure of gases, surface area of solids, temperature, and the presence of a catalyst.
2.How does increasing concentration affect rate, and why?
It increases the rate, because there are more particles in the same volume so collisions are more frequent.
3.How does increasing the pressure of a gas affect rate, and why?
It increases the rate, because the particles are squeezed into a smaller volume so they collide more often.
4.How does increasing surface area affect rate, and why?
It increases the rate, because more of the solid is exposed so there are more places for collisions to happen.
5.Why does a powder react faster than a large lump of the same mass?
The powder has a much greater surface area to volume ratio, so far more particles are available to collide.
6.How does increasing temperature affect rate?
It increases the rate, for two reasons at once.
7.Give both reasons temperature increases rate.
Particles move faster so collide more frequently, and a greater proportion of collisions have at least the activation energy.
8.Which of the two temperature effects is more important?
The increase in the proportion of particles with enough energy has the larger effect.
9.What is a catalyst?
A substance that speeds up a reaction without being used up or changed permanently.
10.How does a catalyst increase the rate?
It provides a different pathway with a lower activation energy, so more collisions are successful.
11.Why is a catalyst not shown in the balanced equation?
It is not used up, so the amount of it is the same before and after the reaction.
12.Give an industrial example of a catalyst.
Iron is used in the Haber process to make ammonia.
13.What are biological catalysts called?
Enzymes.
14.Why do catalysts save money in industry?
They allow a reaction to run fast enough at a lower temperature and pressure, which reduces energy costs.
15.In the disappearing cross practical, what reaction is used?
Sodium thiosulfate reacting with hydrochloric acid, which produces a cloudy yellow precipitate of sulfur.
16.How is the rate measured in that practical?
By timing how long it takes for the cloudiness to hide a cross marked on paper under the flask.
17.What is the independent variable in the disappearing cross practical?
The concentration of the sodium thiosulfate solution, or the temperature.
18.Give a limitation of the disappearing cross method.
Deciding when the cross has disappeared is subjective, so different people would record different times.
19.How could that limitation be reduced?
By using a light sensor and data logger to detect the cloudiness objectively.
20.In the gas volume practical, what reaction is often used?
Magnesium ribbon reacting with hydrochloric acid, producing hydrogen gas.
21.How is the gas collected and measured?
In a gas syringe, or in an inverted measuring cylinder full of water.
22.Name three control variables for the gas volume practical.
The volume of acid, the mass and surface area of the magnesium, and the temperature.
23.Why must the bung be fitted immediately after adding the metal?
Any gas escaping before the bung is in place is not measured, so the readings would be too low.
24.Why should the experiment be repeated?
To calculate a mean, which reduces the effect of random errors and makes the results more reliable.
25.How do you know from a graph that a catalyst has been used?
The line is steeper at the start but levels off at the same final value, because the amount of product is unchanged.
26.Does a catalyst change the amount of product formed?
No. It only changes how quickly that amount is reached.
27.Why does increasing surface area not change the total volume of gas produced?
The amount of reactant is the same, so the same amount of product forms, just faster.
28.Why is temperature the hardest variable to control in these practicals?
Many of the reactions are exothermic, so the mixture warms itself up as the reaction proceeds.
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