First Law Practice

The First Law of Thermodynamics can be summarized by simply saying that all thermodynamic processes follow the principle of the conservation of energy. It can also be captured in a simple equation.

First Law of Thermodynamics

$\mathsf{ \Delta U = Q - W}$

... where U is the internal energy of the system, Q is the heat transferred to or from the system and W is the work done on or by the system.

Use the definition and equation representation of The First Law of Thermodynamics to answer these questions. Be careful, a negative work means you are subtracting a negative!

A total of 123 J of work is done on a gaseous refrigerant while it undergoes compression. If 13 J of heat is released during this process, what is the total change in internal energy of the system?

$\small\mathsf{ \Delta U = Q - W}$

$\small\mathsf{ \Delta U = -13 \text{ J} + 123 \text{ J}}$

$\small\mathsf{ \Delta U = 110 \text{ J}}$

A gas expands when 778 J of heat is added to it. The expanding gas does 498 J of work on its environment. What is the change in internal energy of the gas?

$\small\mathsf{ \Delta U = Q - W}$

$\small\mathsf{ \Delta U = 778 \text{ J} - 498 \text{ J}}$

$\small\mathsf{ \Delta U = 280 \text{ J}}$

A system's internal energy is 47 J before heat is added to the system. If the final internal energy is 68 J and the system does 29 J of work, how much heat is added to the system?

$\small\mathsf{ \Delta U = Q - W}$

$\small\mathsf{ (68 \text{ J} - 47 \text{ J})) = Q - 29 \text{ J}}$

$\small\mathsf{ 21 \text{ J} = Q - 29 \text{ J} }$

$\small\mathsf{ Q = 50 \text{ J} }$

A gas expands when 778 J of heat is added to it. The expanding gas does 498 J of work on its environment. What is the change in internal energy of the gas?

$\small\mathsf{ \Delta U = Q - W}$

$\small\mathsf{ \Delta U = 778 \text{ J} - 498 \text{ J}}$

$\small\mathsf{ \Delta U = 280 \text{ J}}$

Cards remaining: 3

Can you solve these problems using The First Law of Thermodynamics?

Card deck complete!