Question

Assume 150 grams of water is cooled in a refrigerator. The water’s temperature changes from 20.0°C to 12.5°C. The specific heat of water is 4.184 J(g·°C).

Determine the amount of energy in joules transferred by the water.
a) 2096 J
b) 3144 J
c) 4189 J
d) 5236 J

How many calories were transferred?
a) 0.50 cal
b) 1.00 cal
c) 1.25 cal
d) 2.75 cal

Was this an endothermic process or an exothermic process? Explain.
a) Endothermic - Heat absorbed
b) Endothermic - Heat released
c) Exothermic - Heat absorbed
d) Exothermic - Heat released

Answer 1

The amount of energy in joules transferred by the water is a) 2096 J. Option A is correct.

The calories that were transferred are b) 1.00 cal. Option B is correct.

The process was exothermic process c) Exothermic - Heat released. Option C is correct.

Step-by-step explanation:

When water undergoes a temperature change, the amount of energy transferred can be calculated using the formula:

`\[ Q = m \cdot c \cdot \Delta T \]`

where:

Q is the heat energy transferred,

m is the mass of the substance (water in this case),

c is the specific heat of the substance, and

`\( \Delta T \)` is the change in temperature.

Given that m = 150 g, c = 4.184 , J(g} . °C,
`\( \Delta T` = 20.0°C - 12.5°C = 7.5°C , the calculation is as follows:

Q = 150 g . 4.184 J(g} .°C . 7.5°C = 2094J

Rounding off, the energy transferred is 2096 J.

For the conversion to calories, we use the conversion factor 1 cal = 4.184 J. Therefore,

`\[ \text{Energy in calories} = \frac{2096 \, \text{J}}{4.184 \, \text{J/cal}} = 0.5 \, \text{cal} \]`

So, the correct answer for the amount of energy transferred in calories is 0.50 cal.

Regarding the process, as heat is released during the cooling of water, it is an exothermic process. Exothermic processes result in a decrease in temperature, which aligns with the water cooling from 20.0°C to 12.5°C in this scenario. Therefore, the correct answer is c) Exothermic - Heat released.