2 Energy, Heat, and Work Free Online FlashCards

Which energy forms make up a closed system’s total energy?

For a closed system, total energy can be written as $E = U + KE + PE$, including only the forms relevant to the situation.

How can energy cross the boundary of an open system besides heat and work?

In an open system, energy can enter or leave with matter flowing across the system boundary.

What makes an energy transfer heat?

Heat is energy transferred across a boundary because of a temperature difference.

Which way does heat flow spontaneously?

Heat flows spontaneously from higher temperature toward lower temperature.

Is heat a property stored in a system?

Heat describes energy in transfer, not energy stored in a system. After transfer, the energy is part of the receiving system’s energy.

What makes an energy transfer work?

Work is energy transferred across a boundary through an organized interaction other than a temperature difference.

What determines whether energy transfer is heat or work?

Whether energy crosses as heat or work depends on how it crosses the chosen system boundary, not on whether it eventually warms the system.

What is the closed-system first law under this chapter’s sign convention?

With heat positive into the system and work positive when done by it, the first law is $\Delta E = Q - W$.

What signs represent heat and work under this chapter’s convention?

Heat entering the system has $Q > 0$, while heat leaving has $Q < 0$. Work done by the system is positive; work done on it is negative.

How does the first law change if work is positive when done on the system?

If work is defined positive when done on the system, the first law becomes $\Delta E = Q + W_{\text{on}}$. The conventions are equivalent when used consistently.

How is quasistatic pressure–volume boundary work calculated?

For a quasistatic process, boundary work done by the system is $W_{\text{by}} = \int_{V_1}^{V_2} p\,dV$, where $p$ is the system pressure during the process.

What is the sign of work by the system during expansion and compression?

Expansion gives positive work by the system; compression gives negative work by the system.