Solve the following problem: Heat is converted into Work and vice versa, that causes change in internal energy. 1 cal. = 4.184 Joule (J) - is the S.I. unit for energy Formula: AU = Q-W Q=W+AU
1. If 200 J of energy is added to a system when no external work has been done, by how much will the thermal energy of the system be raised?
2. A 100 J of energy is added to a system that does 10 J of external work. By how much is the thermal energy of the system raised?
3. A beaker containing water has 1500 J of work
done on it by stirring and 200 cal of heat
added to it from a hot plate.
What is the change in the internal energy of the
water in Joules?
b. Determine the change in the internal energy of the water in calories.
Answers & Comments
Answer:
1. The increase in thermal energy will be 200 J.
2. The change in internal energy (AU) can be calculated using the formula AU = Q - W. Plugging in the values we get, AU = 100 J - 10 J = 90 J. Therefore, the thermal energy of the system will be raised by 90 J.
3. The change in internal energy (AU) can be calculated using the formula AU = Q - W. Plugging in the values we get, AU = (200 cal x 4.184 J/cal) - 1500 J = -630.64 J. Therefore, the internal energy of the water has decreased by 630.64 J.
b. To convert the change in internal energy into calories, we can use the formula 1 cal = 4.184 J. Plugging in the value we get, -630.64 J ÷ 4.184 J/cal = -150.74 cal. Therefore, the internal energy of the water has decreased by 150.74 cal.