Chapter 10 1 Relationships Between Heat and Work

Chapter 10 -1 Relationships Between Heat and Work January 24, 2017

Internal Energy to Do Work is done when a force is applied an object moves a distance. Since particles have energy and the ability to move, they are able to apply forces which can do work. There are three types of thermodynamic processes we will focus on: 1. Isovolumetric 2. Isothermal 3. Adiabatic

Work can be done on or by a system Generally speaking… • If a gas is compressed, work is being done on the system • If a gas expands, work is being done by the system.

Isovolumetric Processes Definition: a thermodynamic process that takes place at constant volume so that no work is done on or by the system. When a gas undergoes a change in temperature but no change in volume, no work is done on or by the system. For example, heating a gas in a rigid container. The gas gains internal energy, but the volume does not change. Thus, no work was done on or by the gas. Your calorimeter was also an Isovolumetric process.

Isothermal Processes • Definition: a thermodynamic process that takes place at constant temperature. • In an ideal gas, internal energy depends only on temperature; therefore, if temperature does not change, then internal energy cannot change either. Thus, in an isothermal process, internal energy does not change when energy is transferred to or from the system as heat or work. • Boiling water or melting ice are examples of isothermal processes.

Adiabatic Processes • Definition: a thermodynamic process during which no energy is transferred to or from the system as heat • Although adiabatic processes have no net heat change, this doesn’t mean that temperature is constant!

10 -2 First Law of Thermodynamics

First Law of Thermodynamic • There are three Laws of Thermodynamics. We will look at each one individually. • First Law (aka Law of Conservation of Energy): Energy cannot be created or destroyed in an isolated system. • The principle of energy conservation takes into account internal energy, heat, and work done.

When are heat and work positive/negative?

First Law of Thermodynamics Formula *It is important to use the correct signs as discussed on the previous slide. U: Change in Internal Energy (J) Q: Heat (J) W: Work (J)

Example Problem • 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?

Example Problem Solution •

Matching The following boxes are missing their titles. The possible titles are isovolumetric process, isothermal process, adiabatic process, and isolated system. Place the correct title in each box of conditions. Each title is used once.

Problems - Graded • Page 342: #3 -5 • Page 345: #1, 4