THD - First Law of Thermodynamics

First Law of Thermodynamics

Introduction

The first law of thermodynamics states that the change in internal energy in a closed system is equal to the heat added to the system plus the work done on the system.

Mathematically,

When heat is added to the system, Q is +

When heat is removed from the system, Q is -

When work is done on the system, W is +

When work is done by the system, W is -

Since heat flow and work are the primary means by which energy can enter or leave an enclosed system, the first law of thermodynamics is considered to be a broad statement of the law of conservation of energy.

Thermodynamic Processes

For a change in internal, energy to occur, a system must have a change in state. The state of the is defined by the quantities of internal energy, U, pressure, P, volume, V, and temperature, T. You need to be familiar with several thermodynamic processes associated with changing the state of a system.

• Isothermal - A change in state where temperature is kept constant.
• Adiabatic - A change in state where no heat is allowed to flow into or out of the system.
• Isobaric - A change in state where pressure is kept constant.
• Isovolumetric (isochoric) - A change in state where volume is kept constant.

The following presentation will walk you through these processes, and their mathematical implications using the simple example of an ideal gas trapped in a cylinder with a moveable piston.

Thermodynamics Processes Presentation

First Law of Thermodynamics Practice

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