SC18

Question 1

What is activation energy?

Answer 1

The minimum amount of energy needed for a reaction to occur.

Question 2

What are the 4 factors affection reaction rates?

Answer 2

1. Concentration
2. Pressure of gases
3. Surface area
4. Temperature

Question 3

How does the concentration of the solution affect the reaction rate and why?

Answer 3

Increasing the concentration of solutions increases the rate of reaction since there are more reacting particles in the same volume so collisions occur more often.

Question 4

How does the pressure of gases affect the reaction rate and why?

Answer 4

Increasing the pressure of gases increases the rate of reaction since the reactant particles are squeezed closer together so collisions occur more often.

Question 5

How does the surface area affect the reaction rate and why?

Answer 5

Increasing surface area to volume ratio (by decreasing size of solid pieces while keeping total volume of solid the same) increases the rate of reaction since there is more surface for collisions to occur on so collisions occur more often.

Question 6

How does the temperature affect the reaction rate and why?

Answer 6

Increasing the temperature increases the rate of reaction since the reactant particles speed up and have more energy. They collide more often and more particles have enough energy to react when they collide.

Question 7

What is the required apparatus for investigating reaction rates by changing surface area or concentration?

Answer 7

• Large and small marble chips
• Dilute hydrochloric acid
• Collecting tube and bung
• Water trough
• Measuring cylinder (2)
• Clamp and stand/beehive shelf
• Stop clock

Question 8

What is the required apparatus for investigating reaction rates by changing the temperature?

Question 9

What are the 3 methods of investigating reaction rates?

Answer 9

Method 1: Changing surface area
1. Place measuring cylinder in water trough ensuring there are no air bubbles inside
2. Upturn the bottle of the measuring cylinder so the water remains inside and secure it in an upright position using a clamp and stand/beehive shelf
3. Feed the end of the collecting tube under the water and into the open end of the measuring cylinder
4. Measure 5g of large marble chips and put them into a conical flask
5. Use a measuring cylinder to measure 40cm³ of acid and place it into the conical flask
6. Immediately put the bung into the top of the conical flask
7. Measure and record the volume of gas produced every half minute and until no more gas is being produced
8. Repeat the same experiment using small marble chips
9. As small limestone chips have a larger surface area they should finish producing gas more quickly than large chips. A graph should be drawn to compare further.

Method 2: Changing concentration
1. Repeat task 1 using small marble chips of the same mass and same volume acid
2. Change the concentration of acid and record the volume of gas produced in one minute
3. Use concentrations of 0.8, 1.6, 2.4, 3.2 and 4.0 gdm⁻³
4. The higher the concentration the more particles in the same volume of acid. Therefore, there will be more collisions and more successful collisions. This leads to a faster rate of reaction. A graph should be drawn to compare the results

Method 3: Changing temperature