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Question 18N.2.HL.TZ0.b.i

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Date November 2018 Marks available [Maximum mark: 2] Reference code 18N.2.HL.TZ0.b.i
Level HL Paper 2 Time zone TZ0
Command term Calculate Question number b.i Adapted from N/A
b.i.
[Maximum mark: 2]
18N.2.HL.TZ0.b.i

Liquid oxygen at its boiling point is stored in an insulated tank. Gaseous oxygen is produced from the tank when required using an electrical heater placed in the liquid.

The following data are available.

Mass of 1.0 mol of oxygen                                 = 32 g

Specific latent heat of vaporization of oxygen   = 2.1 × 105 J kg–1

An oxygen flow rate of 0.25 mol s–1 is needed.

Calculate, in kW, the heater power required.

[2]

Markscheme

ALTERNATIVE 1:

flow rate of oxygen = 8 «g s−1» ✔

«2.1 × 105 × 8 × 10−3» = 1.7 «kW» ✔

 

ALTERNATIVE 2:

Q = «0.25 × 32 × 10−3 × 2.1 × 105 =» 1680 «J» ✔

power = «1680 W =» 1.7 «kW» ✔

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