First Law of Thermodynamics Quiz

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Questions and Answers

What does the First Law of Thermodynamics state regarding a system's internal energy?

It only considers heat transfer into the system.

It relates the change in internal energy to heat supplied and work done on the system. (correct)

It is independent of work done on the system.

It states that energy cannot be created or destroyed.

In the equation dU = dQ + dW, which of the following statements is true?

dU is considered a function of state. (correct)

dQ must always be negative for work to be positive.

dQ and dW are dependent on the system's initial state.

dW is a function of heat transfer only.

Which limitation is associated with the First Law of Thermodynamics?

It assumes all types of energies are equal. (correct)

It sets a maximum limit on heat transfer.

It provides a specific direction for energy transfer.

It does not take into account the conversion efficiency of work.

If a system experiences a loss of 45 J of heat and 450 J of work is done on it, what will be the change in internal energy?

495 J Signup and view all the answers

What does the First Law of Thermodynamics imply about energy exchange in a system?

It depends only on the initial and final state of the system. Signup and view all the answers

Which statement correctly describes a closed system?

A closed system cannot exchange mass but can exchange energy. Signup and view all the answers

What is an example of a quasi-equilibrium process?

Very slow compression of air in a cylinder. Signup and view all the answers

Which of the following is not a path function?

Potential energy Signup and view all the answers

Match the process with its correct description: What matches Heat to work?

Heat engine Signup and view all the answers

Which of the following is associated with irreversibilities?

Entropy Signup and view all the answers

What does the first law of thermodynamics primarily assert?

Energy cannot be destroyed, only transformed. Signup and view all the answers

If a system’s volume is constant while heat is added, what happens to its internal energy?

It increases. Signup and view all the answers

What is characteristic of an open system?

Allows both mass and energy to cross its boundaries. Signup and view all the answers

Study Notes

First Law of Thermodynamics

The first law of thermodynamics is a statement of the conservation of energy
During interactions, energy can change forms, but the total energy remains constant.
Energy cannot be created or destroyed.
The first law asserts energy is a thermodynamic property.

Learning Goals

Students will be able to recognize basic terminology in thermal engineering.
Students will be able to understand the first law of thermodynamics.

System Definitions

Closed system = control mass
Open system = control volume
Closed system = control mass, a system where the mass remains constant
Open system = control volume, a system where mass can cross the boundary

Quasi-Equilibrium Process

A quasi-equilibrium process is a very slow compression of air in a cylinder.

Path Function vs. State Function (Example)

Not a path function: Thermal conductivity
Examples of path functions: Heat, Work, ∫vdP

Matching Terms (List I to List II):

Heat to work: Heat engine
Heat to lift weight: Hot air balloon
Heat to strain energy: Bimetallic strips
Heat to electromagnetic energy: Thermal radiation

Another Matching Set

Irreversibilities: Thermal equilibrium
Mechanical work: Inexact differences
Zeroth law: High grade energy
Heat: Entropy

The First Law Equation

ΔU = Uf - Ui = Q - W
ΔU = Change in internal energy
Uf = Final internal energy
Ui = Initial internal energy
Q = Heat
W = Work

Sign Conventions (for Q and W)

Positive Q: System gains heat
Negative Q: System loses heat
Positive W: Work done by the system.
Negative W: Work done on the system

Closed System Executing Cycle

Cyclic integral of work = cyclic integral of heat.
∫dW = ∫dQ.

Closed System Undergoing a Process

Total energy entering the system – total energy leaving the system = change in total energy of system
△KE + △PE + △U = Q − W

Energy Balance of a System

The first law of thermodynamics (FLT) is a powerful tool for analyzing energy exchange between a system and its surroundings.
dU = dQ + dW (change in internal energy = heat + work)

Limitations of the First Law

The first law assumes all types of energies are equal.
It does not specify the direction of heat transfer and work transfer.
The first law sets no limit on how much work can be produced from supplied heat.

Total Energy Exchange

The total energy a system exchanges with its surroundings in any process depends only on the initial and final states, not how the change occurred.

Example Problem (Constant Pressure)

A gas loses 45 J of heat to its surroundings and has 450 J of work done onto it. Find the change in internal energy.
ΔU = 495J

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Description

Test your understanding of the first law of thermodynamics, including concepts like energy conservation, closed and open systems, and quasi-equilibrium processes. This quiz will challenge your knowledge of key terminology in thermal engineering and help you distinguish between path and state functions.