Temperature Control and Chocolate Sculptures

Question

Temperature Control and Chocolate Sculptures
A chocolate artist wants to create small chocolate sculptures that can be purchased as gifts for special occasions. She will create the sculptures in a temperature-controlled room within her chocolate shop. Controlling the temperature of the room is necessary because the visual appearance of chocolate can change if it is heated or cooled outside of a specific temperature range. For example, if the chocolate rises above 18°C, the sculpture may begin to melt and change shape. If the chocolate drops below 15°C, the sculpture may begin to discolor as sugar in the chocolate crystallizes and rises to the surface.

The artist wants to design a box to transport the chocolate sculptures when they are delivered. The chocolate shop is located in a city where the temperatures range between 22°C and 30°C all year long. The temperature inside the delivery van is 20°C. The ideal box will be temperature-controlled using a pack that she will design. The pack will hold a chemical substance and 100 grams of water in separate parts of the pack. Squeezing the pack will combine the two substances, causing a chemical reaction to take place that absorbs or releases energy, depending on the substance. The packs will be activated and added to the insulated box and the chocolate sculpture when it is ready to be transported. The box to transport the chocolate sculptures is shown.

The chocolate artist purchases four different substances: ammonium nitrate, calcium chloride, sodium acetate, and sodium hydroxide. She will test the effects of each substance by adding various amounts to the 100 grams of water, then choose one to create the temperature-control packs. The initial temperature of the water before adding the substance is 20° Celsius. The table shows how much the temperature increased or decreased for each substance. A negative (-) in front of the temperature change indicates a decrease in temperature, and a positive (+) indicates an increase. The artist knows that the kinetic energy of the solution decreases as the temperature decreases.

Substance 10 g 20 g 30 g 40 g 50 g
ammonium nitrate -3 -6 -10 -14 -17
calcium chloride +11 +17 +24 +30 +35
sodium acetate -1 -2 -3 -4 -7
sodium hydroxide +12 +20 +29 +35 +41
Multiple Choice Question
Which statement describes the type of chemical reaction that should be used in the temperature-control pack?

A.
The reaction of the pack should absorb thermal energy so that the temperature will decrease when it is activated.

B.
The reaction of the pack should release thermal energy so that the temperature will decrease when it is activated.

C.
The reaction of the pack should absorb thermal energy so that the temperature will increase when it is activated.

D.
The reaction of the pack should release thermal energy so that the temperature will increase when it is activated.

Answer 1

To determine which statement correctly describes the type of chemical reaction that should be used in the temperature-control pack, we need to consider the temperature control requirements for the chocolate sculptures.

The artist has established that temperatures above 18°C can cause the chocolate to melt, and temperatures below 15°C can cause discoloration. Given that the delivery van temperature is 20°C, the ideal solution would be to create a cooling effect to lower the temperature of the box and thus keep the chocolate sculptures from being at risk of melting.

Among the substances tested, only ammonium nitrate and sodium acetate produce a decrease in temperature when mixed with water, indicating that these substances absorb thermal energy.

Thus, the correct statement would be:

A. The reaction of the pack should absorb thermal energy so that the temperature will decrease when it is activated.

This reflects the need to lower the temperature to protect the chocolate sculptures during transportation.