1. Topic 10 Sections 2 and 3

2.  Statement Number Assessment Statement 10.2.1 Deduce an expression for the work involved in a volume change of a gas at constant pressure 10.2.2 State the first law of thermodynamics 10.2.3 Identify the first law of thermodynamics as a statement of the principle of energy conservation 10.2.4 Describe the isochoric (isovolumetric), isobaric, isothermal and adiabatic changes of state of an ideal gas 10.2.5 Draw and annotate thermodynamic processes and cycles on P-V diagrams 10.2.6 Calculate from a P-V diagram the work done in a thermodynamic cycle 10.2.7 Solve problems involving state changes of a gas 10.2 Processes (The First law of Thermodynamics)

3.   By definition: The study of the conditions under which thermal energy can be transferred through performing mechanical work  Macroscopic Properties: Pressure, Volume and Temperature—all used to determine the amount of work that is/can be done by or to a sample of gas. Thermodynamics

4.  Internal Energy

5.   Internal energy of a fixed quantity of a gas (constant number of moles) will only depend on the temperature.  It does NOT depend on volume or pressure  Free-Expansion: when a gas is allowed to expand in a way that is not constricted—both the volume an pressure change in such a way that the temperature will remain constant (in an ideal gas)  Thus—the internal energy is constant for a given temperature of ideal gas. Internal Energy

6.   The complete set of objects being considered in a particular scenario/problem  Open System  Mass is free to enter and/or leave the system  Closed System  Mass is not free to enter and/or leave the system. The quantity of the gas will remain constant  Isolated System  No energy in any form can enter or leave the system Systems

7.   The State of a system is known when particular quantifiable characteristics of the system are known, such as the following:  Pressure  Volume  Temperature  Internal Energy  State Function: a characteristic of the system.  If two gases, originally in different (thermodynamic) states, are brought to the same state, the gases will have the same internal energy—no matter how they got there. State of a System

8.   Thermal Energy and Work  Doing work, or adding or removing thermal energy  Related to a CHANGE in the state, not in the state itself  A gas does not “contain” thermal energy—it can transfer it when it changes state  A gas does not “contain” work—it has work done to it when compressed, or work done by it when expanded Non-state functions

9.  Work Done by/to a Gas  Imagine a Piston—cross sectional area A  Change the position of the piston by applying a force to expand or compress the gas  Volume changes W = P· Δ V

10.  PV diagrams

11.  PV Diagrams  Total work done by the gas as it expands (or to the gas as it’s compressed) = area under the curve  Closed loop? Total (net) work done to/by the system = enclosed area

12.   Those processes in which the pressure of the system remains constant while the volume and temperature change  Results in a horizontal line on a PV diagram (Isobar) Isobaric Processes

13.   Those processes in which the volume remains constant while the pressure and temperature change  Results in a vertical line on the PV diagram (an Isochore)  No work is done during an isochoric process Isochoric Processes

14.   Those processes in which the temperature remains constant (and, as a result, the internal energy)  The pressure and volume will each change Isothermal Process

15.   Thermodynamic Processes are any processes that will result in the change of the state of a system  Heating a gas  Compressing the gas (doing work TO the gas)  Expansion of the gas (work done BY the gas)