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 Form 3 Physics Quantity of Heat Video Questions and Answers

(a) State the meaning of the term “heat capacity.” (1 mark)
(b) State how pressure affects the melting point of a substance. (3 marks)
c) Figure 7 shows a set-up of apparatus that may be used to measure the specific latent heat of vaporization of steam.
figure72132020940.png
(i) Describe how the mass of condensed steam is determined. (3 marks)
(ii) Other than mass and time, state two other measurements that should be taken during the experiment. (2 marks)
(iii) Show how the measurements in (c)(ii) can be used to determine the specific latent heat of vaporization of water. (2 marks)
(iv) State the precautions that should be taken so that the mass of the condensed steamed measured corresponds to the actual mass
of steam collected during the time recorded in the experiment (1 mark)
(v) State why it is not necessary to measure temperature in this set up. (1 mark)

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Answer Text:
a).Heat energy required to raise the temperature of amount of substance by #1^oC# or by 1K.
b).It lowers the melting point.
c).i).The initial mass of an empty well lagged calorimeter is measured, #m_1#.The calorimeter is placed under the delivery tube. After measurable quantity of condensed water is collected the mass of calorimeter +condensed steam is measured #m_2# .Mass of steam =#(m_2 –m_1)g#.
ii).Voltage and current.
iii).Heat supplied by heater = Heat used to vaporize steam.
VIt =#(m_2 – m_1 )L_v#
#L_v = (VIt)/(m_2-m_1)#
iv).Timing and collecting of condensed steam start only when a steady state is reached i.e condensed steam comes out at a constant rate.
v).The temperature remains constant when the boiling water starts to vaporize.


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