# Statements of the Second Law

## Clausius Statement

:
A system operating in a thermodynamic cycle can not transfer energy (heat) from a cooler body to a hotter body and produce no other effect on the universe.

## Kelvin - Planck Statement

:
A system operating in a thermodynamic cycle can not produce a net amount of work while receiving heat from a single thermal reservoir.
Statements of the Second Law of Thermodynamics
The Kelvin-Planck Statement tells us that the efficiency of a heat engine must be less than 100%.
What is the maximum efficiency for a heat engine?
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### Ch 6, Lesson D, Page 1 - Statements of the Second Law

• We introduced the Clausius and Kelvin-Planck Statements of the 2nd Law in the previous lesson.
• In this lesson, we are going to begin to learn why the 2nd Law is so important to the study of thermodynamic cycles.
• We begin with the Kelvin-Planck statement, which tells us that the efficiency of a heat engine must be less than 100%.
• The question that leaps to mind is, exactly how much less ?  Can a heat engine have an efficiency of 99% or is 83% the limit ?
• What is really the upper limit on the efficiency ?
• We will begin to resolve this question in this lesson, but we won’t determine the complete answer until the last lesson of this chapter.
• You’ve got to be patient because there are several new ideas that you need to understand before we can state the upper limit on the efficiency of a heat engine.
• That’s enough foreshadowing for now.  Let’s get started.