Thermodynamics Overview
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Questions and Answers

What happens to the internal energy of a system if heat is added?

  • It stays the same.
  • It increases. (correct)
  • It randomly fluctuates.
  • It decreases.

How is the internal energy of a system affected if work is done by the system?

  • It increases.
  • It decreases. (correct)
  • It remains unchanged.
  • It is completely depleted.

If a gas experiences a loss of heat of 45 J and work of 450 J is done onto the system, what is the change in internal energy?

  • 495 J (correct)
  • 525 J
  • 405 J
  • 405 J

Which statement is true regarding heat leaving a system and its internal energy?

<p>It decreases the internal energy. (B)</p> Signup and view all the answers

In the equation ΔU = Q - W, what does a positive Q indicate?

<p>Heat is added to the system. (A)</p> Signup and view all the answers

What does the first law of thermodynamics state regarding the change in internal energy of a system?

<p>It is equal to the amount of heat supplied to the system minus the amount of work done on its surroundings. (C)</p> Signup and view all the answers

When is the work done by the system considered positive?

<p>When work is done on the surroundings. (B)</p> Signup and view all the answers

In an isothermal process, what is the condition of the change in internal energy?

<p>The internal energy remains constant. (D)</p> Signup and view all the answers

How does an endothermic reaction differ from an exothermic reaction?

<p>Endothermic reactions absorb heat while exothermic reactions release heat. (D)</p> Signup and view all the answers

If a system absorbs 50 J of heat and does 30 J of work on its surroundings, what is the net change in its internal energy?

<p>20 J (A)</p> Signup and view all the answers

What happens to a system during an adiabatic process?

<p>No energy is transferred as heat to or from the system. (A)</p> Signup and view all the answers

What is the result of combining 25 J of heat lost from a system with 4 J of work done on the system?

<p>19 J decrease in internal energy. (A)</p> Signup and view all the answers

If a system undergoes an isolated process, what is the net change in internal energy?

<p>It remains constant. (C)</p> Signup and view all the answers

Flashcards

Internal Energy Change Equation

The change in internal energy (ΔU) of a system is equal to the heat (Q) added to the system minus the work (W) done by the system. The internal energy represents the total energy stored within a system at a given time.

Heat and Internal Energy

When heat is added to a system, its internal energy increases. The system gains energy in the form of heat.

Heat Loss and Internal Energy

When heat leaves a system, its internal energy decreases. The system loses energy in the form of heat.

Work Done BY the System

When a system does work on its surroundings, its internal energy decreases. The system expends energy to perform work.

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Work Done ON the System

When work is done on a system, its internal energy increases. The system gains energy as work is done upon it.

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What is thermodynamics?

The study of how heat and temperature affect other forms of energy.

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What is internal energy?

The amount of energy contained within a system. It is a state function, meaning its value depends only on the current state of the system, not on how it got there.

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What are exothermic reactions?

Reactions that release heat into the surroundings, causing the temperature of the surroundings to increase. This is because the products have lower energy than the reactants.

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What are endothermic reactions?

Reactions that absorb heat from the surroundings, causing the temperature of the surroundings to decrease. This is because the products have higher energy than the reactants.

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What is the first law of thermodynamics?

It states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system.

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In the first law, what does Q (heat) represent?

A positive value means heat is added to the system. A negative value means heat is leaving the system.

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In the first law, what does W (work) represent?

A positive value means work is done by the system. A negative value means work is done on the system.

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What is an adiabatic process?

A process where no heat is exchanged with the surroundings, so the change in internal energy equals the work done.

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Study Notes

Thermodynamics

  • Thermodynamics is the branch of science studying heat, temperature, and their relation to other energy forms.

Competencies

  • Explain the first law of thermodynamics
  • Explain enthalpy of a reaction

Thermochemistry

  • Exothermic: Releases energy (ΔH is negative)
  • Endothermic: Absorbs energy (ΔH is positive)
  • ΔH = change in enthalpy

Change in Enthalpy (ΔH)

  • ΔH = products - reactants
  • Positive ΔH = endothermic reaction
  • Negative ΔH = exothermic reaction

Heat and Work

  • Work can be used to create heat.
  • Heat can be used to create work.

System, Surroundings, and Boundary

  • A system is the specific part of the universe being studied.
  • Surroundings are the rest of the universe outside the system.
  • The boundary separates the system from the surroundings.
  • Internal Energy (U)

Two Types of Reactions

  • Exothermic: A reaction releasing energy in the form of heat from the system.
  • Endothermic: A reaction absorbing energy in the form of heat from the surroundings.

First Law of Thermodynamics

  • The change in internal energy (ΔU) of a system is equal to the heat added (Q) minus the work done by the system (W).
  • ΔU = Q - W
  • Q = heat added to the system
  • W = work done by the system

Sign Conventions

  • Q is positive if heat is added to the system.
  • Q is negative if heat leaves the system.
  • W is positive if work is done by the system.
  • W is negative if work is done on the system.
  • Examples of the first law and sign conventions calculation

Types of processes

  • Isovolumetric: Volume doesn't change, no work done (W = 0)
  • Isothermal: Temperature doesn't change, no change in internal energy (ΔU = 0)
  • Adiabatic: No energy transferred as heat (Q = 0)
  • Isolated system: No energy transferred as heat or work, no change in internal energy (ΔU = Q = W = 0)

Examples

  • Calculation examples for the first law of thermodynamics

Real-life applications

  • Various real-life examples related to the study of thermodynamics are presented to demonstrate the importance of understanding the concept.

Summary

  • If heat is added, internal energy increases.
  • If heat leaves, internal energy decreases.
  • If work is done by the system, internal energy decreases.
  • If work is done on the system, internal energy increases.

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Related Documents

Thermodynamics Lecture Notes PDF

Description

This quiz covers the fundamental concepts of thermodynamics, including the first law, enthalpy changes, and the differences between exothermic and endothermic reactions. Dive into the principles of heat, work, and the interactions within systems and their surroundings to test your understanding of this vital branch of science.

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