Final answer:
To calculate the heat needed to change the temperature of water, we use the formula: heat = mass x specific heat x temperature change. In this case, the heat needed to change the temperature of 100 g of water from -12°C to 18°C is 300 calories.
Step-by-step explanation:
To calculate the heat needed to change the temperature of a substance, we use the formula: heat = mass x specific heat x temperature change. In this case, we have 100 g of water and want to find the heat needed to change its temperature from -12°C to 18°C. Since the temperature change is 18°C - (-12°C) = 30°C, and the specific heat of water is 4.184 J/g °C, we can calculate:
heat = 100 g x 4.184 J/g °C x 30°C = 12552 J
Converting from Joules to calories, we divide by 4.184:
heat in calories = 12552 J / 4.184 J/cal = 2999 cal
Therefore, the correct answer is B. 300 calories.