A catering team tests two identical metal containers of vegetable soup before serving an outdoor event. Each container holds 250 cm3 of soup at 78 degrees C...
Question 1 Report
A catering team tests two identical metal containers of vegetable soup before serving an outdoor event. Each container holds 250 cm3 of soup at 78 degrees C. Container P is fitted with a close lid, while container Q is left open. Both are placed in still air inside separate insulated boxes. A temperature probe records the temperature after 20 minutes. The team also notices droplets on the inside surface of the lid of container P.
Fig. 1 shows the arrangement and the recorded temperatures.
(a) Calculate the temperature decrease of the soup in container P. [2]
(b) Describe the energy transfer that causes the soup in container Q to cool. [2]
(c) Explain why container Q has a lower temperature than container P after 20 minutes. [3]
(d) Give two changes the team could make to reduce the rate of cooling of the soup, other than fitting a lid. [2]
(e) What do the droplets on the lid show has happened to some water vapour? [1]
Answer Details
- (a) \[ \text{temperature decrease}=78-66=12\ ^\circ\text{C} \] The temperature decrease of container P is 12 °C. [2]
- (b) Thermal energy is transferred from the hotter soup to the cooler surroundings. [1] It can be transferred by conduction through the container, convection to the air, or radiation from the surface. [1]
- (c) Container Q allows more water to evaporate. [1] Evaporation requires energy. [1] This energy is taken from the soup, so Q cools more; the lid on P reduces evaporation and also reduces convection. [1]
- (d) Two acceptable changes are: use a thicker insulated box and wrap the container in insulating material. [2] Other acceptable measures include using a smaller-surface-area container, keeping it away from moving air, or placing it in a warmer room.
- (e) The droplets show that water vapour has undergone condensation. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
