R2.2 - how fast? the rate of chemical change

Question 1

What is a rate?

Answer 1

Reciprocal value of time and has the units of s-1

Question 2

What is a rate of reaction?

Answer 2

Change in concentration or a product or a reactant over time. It can be measured by:
- Increase in concentration of products
- Decrease in concentration of reactants
- Measured in mol dm-3 s-1

Question 3

What is a tangent?

Answer 3

Straight line with the same gradient as the point it touches on a gaph.

Question 4

What are the 6 methods of measuring rates of reactions?

Answer 4

1) Change in volume
2) Change in mass
3) Change in the intensity of a specific wavelength of light being absorbed
4) Change in concentration measured using titration (quenching)
5) Change in concentration using conductivity
6) Time for cross to disappear - clock reaction

Question 5

How do you calculate rate of reactions?

Answer 5

1) Increase in product concentration / time
2) Decrease in reactant concentration / time

Question 6

What is the kinetic molecular theory of matter?

Answer 6

Particles in a substance move randomly as a result of kinetic energy that they possess and due to the random nature of these movements and collisions, all particles in a substance will have a range of kinetic energy values.

Question 7

What is absolute temperature?

Answer 7

Lowest temperature when the movement of all particles stop.

Question 8

What is the relationship with temperature and kinetic energy?

Answer 8

As temperature increases, kinetic energy increases; directly proportional relationship.

Question 9

What happens to kinetic energy and temperature as you move from solid to gas?

Answer 9

Temperature and kinetic energy both increase.

Question 10

What is the Maxwell-Boltzmann energy distribution curve?

Answer 10

shows the number of particles having a specific value of kinetic energy against the values of kinetic energy

Question 11

What does the Maxwell-Boltzmann curve tell us about distribution?

Answer 11

• large number of molecules with less energy
• small number of molecules with more energy

Question 12

What is required for a reaction to occur?

Answer 12

• enough energy
  
  • correct orientation

Question 13

What is activation energy?

Answer 13

minimum value of kinetic energy which particles must have so that they can react
- energy is required so that the transition state between reactants and products can occur

Question 14

What 5 factors affect the rate of reaction?

Answer 14

• temperature
• surface area
• pressure
• volume
• catalysts

Question 15

How can temperature affect the rate of reaction?

Answer 15

as temperature increases, the number of molecules that have significant activation energy increases (area under the line to the right increases) and so does kinetic energy
- collision frequency also increases as the particles will be moving faster so there will be more successful collisions

Question 16

How can temperature affect the Maxwell-Boltzmann curve?

Answer 16

The peak shifts to the right, is broader and lower.
- Same area under the curve.
- Majority of the particles have higher energy.

Question 17

How can concentration affect the rate of reaction?

Answer 17

Increasing concentration increases the rate of reaction as the particles are closer together and the frequency of successful collisions increases.
However, as the reaction proceeds, the rate slows down as concentration drops when the reactants are being used up.

Question 18

How can concentration change be seen in a graph?

Answer 18

Lower concentration:
- Less product made, so a lower plateau.
- Less steep gradient
Higher concentration:
- More product made, so a higher plateau.
- More steep gradient

Question 19

How can pressure affect the rate of reaction?

Answer 19

Increasing pressure increases the rate of reaction as the particles are closer together, meaning there is less space in the container and the frequency of successful collisions increases.
- Only occurs in gases.

Question 20

How can pressure change be seen on a graph?

Answer 20

• same amount of product made
• less steep for a lower pressure

Question 21

How can surface area affect the rate of reaction?

Answer 21

smaller solids –> surface area increases
- this means that there is a larger surface area for particles to collide on, increasing the chance of successful collisions and the rate of reaction

Question 22

How can surface area change be seen in a graph?

Answer 22

• Same amount of product made
• Smaller surface area - less steep gradient
• Larger surface area - more steep gradient

Question 23

How can catalysts affect the rate of reaction?

Answer 23

Catalysts increase the rate of a reaction without being used up by providing an alternate reaction pathway with a lower activation energy, causing the frequency of successful collisions to increase and the rate increases as more collisions occur with greater than minimum energy needed to overcome the activation energy barrier.

Question 24

How can catalysts be seen on the Maxwell-Boltzmann curve?

Answer 24

Shifts the activation energy line to the left, so more particles have sufficient energy to react.

Question 25

What are systematic errors?

Answer 25

When all measurements are higher or lower than the expected value.

Question 26

What are random errors?

Answer 26

Errors in individual measurements due to equipment, changes in surrounding, human error, misinterpreted results or insufficient number of trials.