P2C18 - Rates of reaction

Question 1

What must happen for a chemical reaction to take place?

Answer 1

The colliding of particles

Question 2

What is activation energy?

Answer 2

The minimum amount of energy particles need in order to collide.

Question 3

What are the 4 main factors affecting rates of reaction?

Answer 3

Temperature
Concentration
Pressure (gases only)
Surface area

Question 4

What is the collision theory?

Answer 4

The theory that explains how reactions occur and why they occur at different rates.

Question 5

How do you work out rates of reaction at a specific time using a graph?

Answer 5

Draw a tangent to the curve.
Work out the gradient of the tangent:
Rate of reaction = change in y / change in x

Question 6

What are key features of a concentration-time graph?

Answer 6

Plateauing gradient - Slower rate of reaction
Steep gradient - Faster rate of reaction
Zero gradient - Reaction finished

Question 7

What are the key factors that can affect rate of reaction?

Answer 7

• Concentration of dissolved reactants (High=frequent collisions)
• Pressure of gas reactants (High=frequent collisions)
• Temperature (More energy than activation energy=frequent collisions)
• Surface area of solid reactants
• Catalysts

Question 8

What are some examples of catalysts?

Answer 8

Iron - used in the process that makes ammonia.
Platinum and palladium - used in catalytic converters in cars.
Enzymes - catalyse reactions in biological systems.

Question 8

What is a catalyst?

Answer 8

Something that speeds up a reaction without getting used up

Question 9

What are the steps to measuring gas production?
(Rate of Reaction practical)

Answer 9

1. Set up equipment (beaker, conical flask, delivery tube, tank of water, measuring cylinder)
   Make sure the measuring cylinder is full with water.
2. Place in marble chips. The surface area is the independent variable.
3. Pour in hydrochloric acid
4. Start the timer.
5. Record volume of gas produced every 5 seconds. This is the dependent variable.
6. Plot a graph of time against volume of gas.
   Draw a curve of best fit.
7. Calculate the gradient to find rate at different times.

Question 10

What do you do in the colour changing practical?
(Rate of reaction)

Answer 10

1. Set up the ​equipment (Conical flask, paper with an X under flask)
2. Place the solutions (except acid) in beakers.
3. Pour in acid (this is the independent variable) and start the stop clock.
4. Stop the clock when the cross cannot be seen. (Time taken is dependent variable.)
5. Repeat for different concentrations of acid.
6. Plot a graph of time against concentration of acid.
7. Draw line of best fit.
8. Calculate the gradient to find how the rate changes per increase in concentration.