Chapter 10: Section 2. Describe the First Law of Thermodynamics Make calculations involving changes in internal energy Create and analyze energy.

Chapter 10: Section 2

Describe the First Law of Thermodynamics Make calculations involving changes in

internal energy Create and analyze energy transfer

diagrams

Imagine a roller coaster that operates on a frictionless track

Work, a force that causes a displacement, is initially necessary to raise the car against the gravitational force.◦Once the car is freely moving, it will have a

certain kinetic and potential energy With no friction, the mechanical energy (KE

+ PE) will remain constant

If friction is taken into account, mechanical energy is no longer conserved

A steady decrease in the coaster’s total mechanical energy occurs because of work being done against friction

Mechanical energy is transferred to particles throughout the entire coaster◦The increases in internal energy equal the

decreases in mechanical energy Most of this energy is gradually lost to the

air as heat◦If the internal energy of the roller coaster

and the energy dissipated to the surrounding air are taken into account, the total energy will be constant

The principle of energy conservation that takes into account internal energy as well as work and heat is called the First Law of Thermodynamics

The First Law says that energy cannot be created nor destroyed.

In terms of a machine, this means that the total energy output (work done by the machine) is equal to the heat supplied.

In other words, the change in the internal energy of a closed system is equal to the heat added to the system minus the work done by the system.◦ If all of the heat supplied to the system (Q) is

transformed into work (W), then the change in total internal energy should be zero

∆U = Q – W Because the system operates in the real

world, some energy always escapes into the outside world

A total of 135 J of work is done on a gaseous refrigerant as it undergoes compression. If the internal energy of the gas increases by 114 J during the process, what is the total amount of energy transferred as heat? Has energy been added to or removed from the refrigerant as heat? ◦-21 J ◦Energy is removed

Energy transfer diagrams show the locations of energy stores and energy transfers.

For example, consider the energy transfers in a simple electrical circuit.

The battery is a store of chemical energy. The energy is transferred by electricity to

the lamp, which transfers the energy to the surroundings by light.