Using calorimetry

Question 1

What is calorimetry used for?

Answer 1

finding the energy in a sample of food

Question 2

steps to calorimetry

Answer 2

1) the temperature of water in a test tube at the start is measured
2) the mass of the food sample is measured
3) the food is set alight and placed immediately under the tube
4) the temperature of the water at the end is measured, and the change in temperature is calculated

Question 3

Describe the setup used for calorimetry

Answer 3

a clamp stand is used to suspend a test tube containing water and a thermometer over a mounted needle that holds the food sample

Question 4

How does the burning of the food sample increase the temperature of the water?

Answer 4

the energy released from burning the food is transferred to the water

as the water gains energy its temperature increases

Question 5

What variable is the control in the experiment?

Answer 5

the calorimeter (test tube) contains a measured volume of water

Question 6

How much energy does it take to increase the temperature of 1 cm[3] of water by 1 C?

Answer 6

4.2 J

Question 7

A student burns 2g of a cereal bar underneath a test tube containing 20 cm[3] of water

The water temperature was 16 C at the start, but increases to 34 C

If the whole cereal bar is 125 g, how much energy does it contain?

Answer 7

34 - 16 = 18 C rise in temperature

20 x 18 x 4.2 J = 1.512 kJ

1. 512 kJ/2 = 0.756 kJ in 1g
2. 756 x 125 = 94.5 kJ

Question 8

A student used calorimetry to measure the energy in a potato snack. The test tube contained 10 cm[3] water. Give two reasons why this might not be an accurate measurement. [2]

Answer 8

taking too long to move the burning food to under the tube

holding the food at different distances from the tube

this would affect how much energy is transferred to the surrounding air and not the tube

• not measuring the mass of food/initial temp/volume of water accurately
• the food not burning completely

Question 9

a) 200g of potato crisps were burned in a bomb calorimeter

this raised the temperature of 500 cm[3] water by 2 C.

it takes 4.2 J of energy to raise the temp of 1 cm[3] of water by 1 C.

find the energy in 100g crisps, show your working [2]

b) calculate the energy in 1g of crisps [1]

Answer 9

a) 500 x 4.2 x 2 = 4200 J

b) 4200/200 = 21 J