Question
During an isothermal expansion, a confined ideal gas does $$-150\,J$$ of work against its surroundings. This implies that
A.
$$300\,J$$ of heat has been added to the gas
B.
no heat is transferred because the process is isothermal
C.
$$150\,J$$ of heat has been added to the gas
D.
$$150\,J$$ of heat has been removed from the gas
Answer :
$$150\,J$$ of heat has been added to the gas
Solution :
Concept
Apply first law of thermodynamics. According to first law of thermodynamics
$$\Delta U = \Delta Q + \Delta W$$
For isothermal process, $$\Delta U = 0$$
So, $$\Delta Q = - \Delta W$$
Given, $$\Delta W = - 150\,J$$
So, $$\Delta Q = + 150\,J$$
When $$Q$$ is positive, the heat is added to the gas.