R2.2 How Fast? The rate of chemical change

Question 1

Define the term rate of reaction: (1)

Answer 1

• The speed at which a chemical reaction takes place. (1)

Question 2

State the formula regarding rate of reaction: (1)

Answer 2

• Change in concentration/time (c/t) (1)

Question 3

State what happens to the rate of reaction as the gradient gets steeper: (1)

Answer 3

• The rate of reaction increases. (1)

Question 4

Explain how colorimetry is used to measure the rate of reaction: (4)

Answer 4

• The solution must be coloured. (1)
• This happens naturally or a drop of indicator is added to generate a coloured compound. (1)
• The light of a specific wavelength is is passed through the solution (1)
• It measures the light intensity of the light transmitted by the reaction components. (1)

Question 5

Explain how changes in mass can be used to measure the rate of a reaction: (3)

Answer 5

• When a gas is produced, it escapes from the reaction vessel. (1)
• So the mass of the vessel decreases. (1)
• This allows the change in mass to be recorded. (1)

Question 6

Describe 2 limitations of using changes in mass to measure the rate of a reaction: (2)

Answer 6

• The gas must be sufficiently dense. (1)
• The mass is too small to measure on a 2 or 3 decimal balance. (1)

Question 7

Explain how volume of gases can be used to measure the rate of a reaction: (2)

Answer 7

• A gas syringe can be used. (1)
• When a gas is produced, it can be trapped so its volume can be measured. (1)

Question 8

Explain how gases with a low water solubility can be used to measure rate of reaction. (2)

Answer 8

• The gas can be collected through water by a displacement. (1)
• Using an inverted measuring cylinder or burette. (1)

Question 9

Describe how measuring concentration changes during titration can affect the rate of reaction: (1)

Answer 9

• Tbe act of taking a sample can disrupt the reaction. (1)

Question 10

Explain how to take a sample from a titration reaction without disrupting it: (2)

Answer 10

• Through quenching (1)
• Quenching freezes the reaction at a specific point to allow the concentration to be determined. (1)

Question 11

Explain how conductivity can be used to measure the rate of a reaction: (2)

Answer 11

• As the reaction proceeds, the concentration of ions may change which affects the conductivity. (1)
• By measuring conductivity at different times, the rate of reaction can be determined based on how quickly the conductivity changes. (1)

Question 12

Describe how to measure a clock reaction: (1)

Answer 12

• Measure the time taken to reach a fixed point in a reaction (e.g when something goes milky) (1)

Question 13

State the relationship between kinetic energy and temperature in kelvin as particles: (1)

Answer 13

• Directly proportional (1)

Question 14

Describe the concept of collision geometry: (2)

Answer 14

• Particles have to have the correct orientation when they collide to be successful. (1)
• In order for a reaction to occur. (1)

Question 15

Explain the effect of increasing concentration on the rate of reaction: (4)

Answer 15

• The higher the concentration, the greater the number of particles in a solvent. (1)
• This results in an increase in collision frequency. (1)
• Therefore the frequency of successful collisions increases. (1)
• This increases the rate of reaction. (1)

Question 16

Explain the effect of increasing pressure on the rate of reaction: (4)

Answer 16

• When the pressure increased, particles have less space to move. (1)
• This means that there is an increase in collision frequency. (1)
• This increases the frequency of successful collisions. (1)
• This increases the rate of reaction. (1)

Question 17

Explain the effect of increasing temperature on the rate of reaction: (5)

Answer 17

• As the temperature increases, the particles move faster. (1)
• So collision frequency increases. (1)
• The particles also meet the activation energy. (1)
• So this increases the proportion of successful collisions. (1)
• Therefore the rate of reaction increases. (1)

Question 18

Explain the effect of increasing surface area on the rate of reaction: (4)

Answer 18

• If the surface area increases, there are more particles on the surface. (1)
• This means that there are more particles for collision so the collision frequency increases. (1)
• This means that more successful collisions takes place. (1)
• This increases the rate of reaction. (1)

Question 19

Explain the effect of a catalyst on the rate of reaction: (3)

Answer 19

• It provides and alternative reaction pathway. (1)
• This increases the frequency of successful collisions between particles. (1)
• This increases the rate of reaction. (1)

Question 20

Define the following terms: (3)

• Unimolecular (1)
• Biomolecular (1)
• Termolecular (1)

Answer 20

• When one reactant particle is involved in the elementary step. (1)
• When two reactant particles are involved in the elementary step. (1)
• When 3 reactant particles are involved in the elementary step. (1)

Question 21

State the formula to calculate activation energy: (1)

Answer 21

ln(k1/k2) = Ea/R (1/T2 - 1/T1) (1)