Question

Heat and Work UE:6 days Assigned as tomewor HQ5.15 The air in an inflated balloon (the system) absorbs 125 J of heat from its proximity to a fire. The balloon expands and does 85 kJ of work. What is the change in internal energy (in (AU) for the system? (Do not include units in your answer) Numeric Answer 2 attempts left Unanswered 3:14 PM OeO 22018 DOLL

Answer 1

INTRODUCTION: The sign convention for heat flow are as follows: When the heat flows into the system, a positive sign is assigned. When the heat flows out of the system, a negative sign is assigned. The sign convention for work are as follows: When the work is done on the system, a positive sign is assigned. When the work is done by the system, a negative sign is assigned. The sign convention for internal energy change (AE) are as follows: When the energy is absorbed by the system, a positive sign is assigned. When the energy is released by the system, a negative sign is assigned. According to the first law of thermodynamics: dU =q+w .....(i) Here, dU is the change in internal energy, is the heat flow, and w is the work done. SOLUTION: According to the question, the balloon is absorbing 125 J of heat, thus, q= + 125 J. According to the question, the balloon is expanding and does a work of 85 kJ on its surroundings. Thus, the work done will be w=- 85 kJ. Substitute these values in equation (i) to calculate the internal energy change as shown below: 7:1 kJ =109 dU =q+w =125 5 –85000 J =-84,875 J =-84.875 kJ [:15=10-9 kJ] Hence, the change in internal energy for the given system is - 875