Question

A 1.5 grams sample of rice is placed in a calorimeter. When the sample is burned, the rice's energy value is 2.81 kcal/g. How many kilojoules of heat are given off by the rice?

a) 11.73 kJ

b) 4.22 kJ

c) 0.00281 kJ

d) 2810 kJ

Answer 1

The heat given off by the 1.5 grams of rice when burned is approximately 17.64 kJ, after calculating the total energy in kcal and converting it to kJ.

Step-by-step explanation:

When a 1.5 grams sample of rice is burned yielding an energy value of 2.81 kcal/g, we can calculate the total energy released in kilocalories and then convert it to kilojoules using the conversion factor 1 cal = 4.184 J. By multiplying the mass of the rice by the energy value per gram, we find the total energy released in kilocalories and convert this amount to kilojoules as follows:

Total energy (kcal) = 1.5 g × 2.81 kcal/g = 4.215 kcal

Total energy (kJ) = 4.215 kcal × 4.184 kJ/kcal = 17.6396 kJ

Therefore, the heat given off by the rice is approximately 17.64 kJ, which is not one of the options provided. This indicates a possible mistake in the proposed answer choices or in the data given.

Answer 2

The amount of heat released by burning a 1.5g sample of rice with an energy value of 2.81 kcal/g is 17.64 kJ. This is calculated by first finding the heat in kilocalories (4.215 kcal) and then converting to kilojoules using the conversion factor 1 kcal = 4.184 kJ.

Step-by-step explanation:

The subject of this question is how to calculate the amount of heat given off by a sample of rice when burned, measured in kilojoules. The rice sample has a mass of 1.5 grams and an energy value of 2.81 kcal/g. To find the total amount of heat released in kilocalories, we multiply the mass of the rice by its energy value: 1.5g × 2.81 kcal/g = 4.215 kcal. To convert this value into kilojoules, we use the conversion factor 1 kcal = 4.184 kJ:

4.215 kcal × 4.184 kJ/kcal = 17.6426 kJ

Therefore, the answer is 17.64 kJ (rounded to two decimal places), which is not one of the given options. It appears there may have been an error in the listed options. The correct answer would be closest to option (a) 11.73 kJ, but this is not exact.