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Question 23M.2.SL.TZ1.2

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Date May 2023 Marks available [Maximum mark: 7] Reference code 23M.2.SL.TZ1.2
Level SL Paper 2 Time zone TZ1
Command term Compare, Estimate, Show Question number 2 Adapted from N/A
2.
[Maximum mark: 7]
23M.2.SL.TZ1.2

A solid piece of chocolate of mass 82 g is placed in a pan over fire. Thermal energy is transferred to the chocolate at a constant rate. The graph shows the variation with time t, of the temperature T of the chocolate. At 6.0 minutes all the chocolate has melted.

The specific heat capacity of solid chocolate is 1.6 × 103 J kg−1 K−1.

(a)

Show that the average rate at which thermal energy is transferred into the chocolate is about 15 W.

[3]

Markscheme

Reads change in temperature to be 45 − 31 OR 14 °C ✓


Q = 0.082 × 1.6 × 103 × 14 = 1.84 × 103 «J» ✓

P = 1.84×1032.0×60 = 15.3 ≈ 15 «W»✓

 

Must see either full substitution OR answer to at least 3 s.f. in MP3

(b)

Estimate the specific latent heat of fusion of chocolate.

[2]

Markscheme

Q = 15.3 × 4.0 × 60 = 3.67 × 103 «J» ✓

L = 3.67×1030.082 = 4.5 × 104 «J kg−1» ✓

 

Allow ECF from MP1

(c)

Compare the internal energy of the chocolate at t = 2 minutes with that at t = 6 minutes.

[2]

Markscheme

Internal energy is greater at t = 6 min OR internal energy is lower at t = 2 min OR internal energy increases «as energy is added to the system» ✓

Because kinetic energy «of the molecules» is the same AND potential energy «of the molecules» has increased / OWTTE ✓

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