Question 18N.2.HL.TZ0.9
| Date | November 2018 | Marks available | [Maximum mark: 7] | Reference code | 18N.2.HL.TZ0.9 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Distinguish, State | Question number | 9 | Adapted from | N/A |
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
Distinguish between the internal energy of the oxygen at the boiling point when it is in its liquid phase and when it is in its gas phase.
[2]
Internal energy is the sum of all the PEs and KEs of the molecules (of the oxygen) ✔
PE of molecules in gaseous state is zero ✔
(At boiling point) average KE of molecules in gas and liquid is the same ✔
gases have a higher internal energy ✔
Molecules/particles/atoms must be included once, if not, award [1 max]
An oxygen flow rate of 0.25 mol s–1 is needed.
Calculate, in kW, the heater power required.
[2]
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» ✔
Calculate the volume of the oxygen produced in one second when it is allowed to expand to a pressure of 0.11 MPa and to reach a temperature of –13 °C.
[2]
T = 260 «K» ✔
V = «» 4.9 × 10−3 «m3» ✔
State one assumption of the kinetic model of an ideal gas that does not apply to oxygen.
[1]
ideal gas has point objects ✔
no intermolecular forces ✔
non liquefaction ✔
ideal gas assumes monatomic particles ✔
the collisions between particles are elastic ✔
Allow the opposite statements if they are clearly made about oxygen eg oxygen/this can be liquified
