shc and latent heat (topic 3)

Question 1

mary found it took 15.5 hours for the hot tub to reach 38°C, suggest why the time recorded is much higher than the calculated value (2)

Answer 1

• the heater may not be 100 % efficient and could output less than 3 kW
• energy from the hot tub may be lost to the surroundings

Question 2

suggest two ways Mary might reduce the time it takes to heat the hot tub without using a different hose (2)

Answer 2

• put a lid on the hot tub whilst heating to prevent heat loss by convection
• ensure the walls of the hot tub are wrapped in insulating material

Question 3

a homeowner has 4 of these panel installed on their roof, calculate the energy incident per second on the solar panel array
area = 1.08m^2

Answer 3

Question 4

the array of panels contains 240 kg of water combined, calculate the temperature change of the water when exposed to the sun for 2 hours

Answer 4

Question 5

describe what happens to the arrangement and motion of the particles within the acid as it freezes (2)

Answer 5

• particles move from a more random structure into a regular/uniform arrangement
• particles stop being able to slide past one another, and vibrate about fixed positions

Question 6

the mass of stearic acid used was 50 g and the specific heat capacity of stearic acid is 2,300 J/kg°C, calculate the energy transferred between 0 s and 30 s

Answer 6

Question 7

in step 4 of the students method, the heater is turned off and the temperature recorded, explain why is this incorrect (2)

Answer 7

• when the heater is turned off the temperature will continue to rise
• the student should observe and record the highest temperature reached after the heater is turned off

Question 8

the current through the circuit was 3 A, calculate the energy transferred by the 12 V heater during the 10 minutes it was turned on

Answer 8

Question 9

explain why the calculated value of specific heat capacity (2846j/kg) is different to the accepted value (2460j/kg), you should refer to the students method in your answer

Answer 9

Question 10

describe what is meant by thermal equilibrium (2)

Answer 10

• the temperature will remain constant
• the energy gained by the iron from the water is equal to the energy transferred to the water from the iron
• the net transfer of energy between the iron and water is zero

Question 11

describe what happens to the internal energy of the water as it boils (3)

Answer 11

• the internal energy increases
• the kinetic energy of the water remains constant during the change of state
• the potential energy of the water increases as it changes state from liquid into gas

Question 12

describe how the internal energy of the ice cream varies with time between 0s and 80s (3)

Answer 12

• the internal energy increases with time
• internal energy = kinetic energy + potential energy
• between 0 s and 40 s, the kinetic energy increases but potential energy remains constant
• between 40 s and 80 s, the kinetic energy remains constant and the potential energy increases