Energy and the First Law of Thermodynamics – Lecture Review

Flashcards covering definitions, units, system types, state functions, the First Law, sign conventions, and example applications from the lecture.

What does thermodynamics study?

The general study of energy and its interconversions.

What is energy (E) in thermodynamics?

The capacity to do work.

What are the two ways that energy can be exchanged between objects?

Heat and work.

Define kinetic energy.

Energy of motion, or energy that is being transferred.

Define potential energy.

Energy stored in an object or associated with its composition and position.

Which kind of energy is associated with motion—kinetic or potential?

Kinetic energy.

Which kind of energy is associated with composition or position—kinetic or potential?

Potential energy.

What is the SI unit of energy?

The joule (J).

What non-SI energy unit is commonly used in nutrition labels?

The calorie (cal).

In thermodynamics, what is meant by the system?

The area of investigation.

In thermodynamics, what are the surroundings?

Everything outside the system.

Describe an open system.

A system that allows both mass and energy to cross its boundary.

Describe a closed system.

A system that allows energy but not mass to cross its boundary.

Describe an isolated system.

A system that allows neither mass nor energy to cross its boundary.

What is a state function?

A property that depends only on the initial and final states of the system, not on the path taken.

Define an extensive property.

A property whose value depends on the amount of substance present.

Define an intensive property.

A property that is independent of the amount of substance present.

State the First Law of Thermodynamics.

Energy can neither be created nor destroyed; it can only be transferred or converted from one form to another.

What is internal energy (U)?

The sum of the kinetic and potential energies of all particles in a system.

Is internal energy a state function or a path function?

A state function.

Under thermodynamic sign conventions, when is heat (q) positive?

When heat flows into the system from the surroundings.

Under thermodynamic sign conventions, when is work (w) negative?

When the system does work on the surroundings.

When sweat evaporates from skin (system = sweat), is the energy transfer mainly heat or work, and what is the sign of q?

Heat; q is positive because the sweat absorbs heat.

When a balloon expands against external pressure (system = gas in balloon), is the energy transfer mainly heat or work, and what is the sign of w?

Work; w is negative because the system does work on the surroundings.