C8: Rates Of Reaction

Question 1

List the factors which affect rates of chemical reactions

Answer 1

• Pressure
• Surface Area
• Heat
• Concentration
• Catalyst

Question 2

What is collision theory?

Answer 2

Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy

Question 3

What is the activation energy?

Answer 3

the minimum amount of energy that particles must have to react

Question 4

Why does increasing the temperature increase the rate of reaction?

Answer 4

Increasing the temperature increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction.

Question 5

What is a catalyst?

Answer 5

Catalysts are substances that speed up chemical reactions without being changed or used up during the reaction.

Question 6

How do catalysts increase the rate of reaction?

Answer 6

• Catalysts decrease the actuvation energy; this
  increases the proportion of particles with energy to react.
• Catalysts provide a alternate pathway for a chemical reaction that has a lower activation energy.

Question 7

What is the effect of changing concentration?

Answer 7

An increase in concentration increases the rate of reaction due to a greater number of collisions between reacting particles.

Question 8

How do you calculate the rate of reaction?

Answer 8

Quantity of reactant used/ time

Or

Quantity of product formed/ time

Question 9

What are the units for rate if reaction?

Answer 9

Grams/s pr cm^3/s

Question 10

What is the method for measuring gas volume?

Answer 10

The gradient of this graph will be equal to the reaction rate. The steeper the graph the faster the reaction.
Method 1: Conical flask, gas syringe and cork
Method 2: Conical flask, delivery tube, cork, trough with water and an inverted measuring cylinder

Question 11

What is the method of measuring mass loss?

Answer 11

Place the conical flask with the mixture and cotton on a weighing scale and measure it. As the reaction proceeds, measure the volume of gas lost.

Question 12

What is a different way of measuring rate of reaction and what equipment is used?

Answer 12

Time for a solution to become opaque or coloured:

Conical flask, dilute acid added to a transparent solution and a cross beneath the flask. Wait for the cross beneath the flask to not be visible and time how long this takes.

Question 13

How do you calculate the mean rate of reaction?

Answer 13

Change in volume / change in time

Question 14

How do you find the rate of reaction at a specific time?

Answer 14

Using the gradient of the curve at the time. Find the gradient using:
The difference in y (vertical) / difference in x (horizontal). The tangent’s hypotenus must only touch the singular point.

Question 15

Explain the reuslts that may be obtained at different temperatures using particle theory

Answer 15

The result of a higher temperature shows a steeper gradient as due to an increase of heat, particles have more kinetic enegry, resulting in a higher frequency of collisions as collisions have more energy resulting in more passing the activation energy, speeding up the rate of reaction. Furthermore, the result of the higher temperature finishes earlier as the reaction is much quicker however an equal volume of gas is released as there are equal volumes of magnesium.

Question 16

How does surface area increase the rate of reaction?

Answer 16

A larger surface area provides more space for the reacting particles to collid. This increases the chance of successful collisions and frequency of collision, so a faster rate of reaction.