Answer to Question #304121 in Physics for shan

Question

When gasoline burns in an automobile engine, the heat released causes the product CO₂ and H2O to expand,which pushes the piston outward. if the expanding gases do 789 J of water on the piston and the system loses 245 J of heat, calculate $\Delta U$ in J

Answer 1

According to the first law of thermodynamics, the change in internal energy is given as follows:

$$\Delta U = \delta Q-\delta W$$

where $\delta Q$ is the heat gained by the system (negative, if system looses heat) and $\delta W$ is the work done by the gases. Thus, obtain:

$$\Delta U = -245J-789J = -1034J$$

Answer. -1034J.