[10.1] reaction rates

Question 1

what is a rate of reaction?

Answer 1

• how fast a product is being made
• how fast a reactant is being used up

Question 2

what are the standard units for a solution, solid, and gas?

Answer 2

• solution: mol dm⁻³ s⁻¹
• solid: g s⁻¹
• gas: cm⁻³ s⁻¹

or times other than s

Question 3

how do you use a graph to determine the rate of reaction at a particular point?

Answer 3

• draw a tangent
• calculate gradient (change in y / change in x)

Question 4

describe what happens at 3 points on a graph showing the rate of reaction

Answer 4

1. rate of reaction is fastest at the start of the reaction as each reactant is at its highest concentration (steep curve)
2. rate of reaction slows down as the reaction proceeds because the reactants are being used up and their concentration decreases (curve becomes less steep)
3. once one of the reactants has been completely used up, the concentration stops changing and the rate of reaction is zero

Question 5

what factors affect the rate of reaction? [5]

Answer 5

• surface area of solids
• concentration of solutions
• pressure of gases
• temperature
• catalyst

Question 6

what does collision theory state?

Answer 6

that two reacting particles must collide for a reaction to occur

Question 7

what is needed for an effective collision, which leads to a chemical reaction?

Answer 7

• particles collide with the correct orientation
• particles collide with sufficient energy to overcome the activation energy

Question 8

how does rate of reaction change (if temperature increases)?

Answer 8

• kinetic energy of particles increases
• more frequent successful collision
• successful collisions are ones where the particles are in the correct orientation and have sufficient energy to overcome the activation energy

Question 9

how does increasing the concentration affect the rate of reaction?

Answer 9

• increases the number of particles in the same volume
• particles are closer together and collide more frequently and successfully
• successful collisions are ones where the particles are in the correct orientation and have sufficient energy to overcome the activation energy

Question 10

how does increasing the pressure of a gas affect the rate of reaction?

Answer 10

• when a gas is compressed into a smaller volume the pressure of a gas is increased and the rate of reaction increases
• the concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume
• the gas molecules are closer together and have more frequent successful collisions in the same time
• successful collisions are ones where the particles are in the correct orientation and have sufficient energy to overcome the activation energy

Question 11

how does adding a catalyst increase the rate of reaction?

Answer 11

• catalysts provide an alternative route with lower activation energy
• a greater proportion of reactants have energy greater than the activation energy
• increases the frequency of successful collision
• successful collisions are ones where the particles are in the correct orientation and have sufficient energy to overcome the activation energy
• increases rate of reaction

Question 12

how can the progress of a chemical reaction be followed by?

Answer 12

• monitoring the removal (decrease in concentration) of a reactant
• following the formation (increase in concentration) of a product

Question 13

what can be measured to follow the progress of a reaction?

Answer 13

• gas volume (monitoring the volume of gas produced at regular intervals using gas collection)
• monitoring the loss of mass of reactants or products using a balance

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