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Section 11­1.notebook
February 28, 2012
Work can transfer energy to a substance which increases the internal energy of the substance. Internal energy can then decrease through the transfer of energy as heat. Energy can be transferred to a substance as heat and from the substance as work.
Internal energy of a substance has been treated as a single quantity to which energy is added or taken away. Such a substance is a system.
System ­ a collection of matter within a clearly defined boundary across which no matter passes.
All parts of a system are in thermal equilibrium with each other before and after a process adds or removes energy.
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Section 11­1.notebook
February 28, 2012
An example of a system would be a flask with water and a balloon on the end of the flask. The flask is heated and the temperature of the water increases. Eventually increasing the volume of the balloon. The system of the flask and balloon are treated as being isolated but most often are not. There is energy and heat transferred to the surroundings or enviroment.
Enviroment ­ everything outside a system that can affect or be affected by the system's behavior.
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Section 11­1.notebook
February 28, 2012
Work is the product of a force applied to an object and the distance moved by that object in the direction of the force.
In thermodynamics work is the product of the change in the volume of a gas and the pressure applied on or by the gas. Defining Work in terms of Changing Volume
W = Fd
work = force x distance
W = Fd(A) = (F) (Ad) = PΔV
(A) (A)
work = pressure x volume changes
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Section 11­1.notebook
February 28, 2012
If a gas expands ΔV is positive and the work done on the gas is positive.
If a gas is compressed ΔV is negative and the work done by the gas is negative. When the volume remains constant there is no displacement and no work done on or by the system.
An engine cylinder has a cross­sectional area of 0.010 m2. How much work can be done by a gas in the cylinder if the gas exerts a constant pressure of 7.5 x 105 Pa on the piston and moves the piston a distance of 0.040 m? 4
Section 11­1.notebook
February 28, 2012
Three distinct quatities have been related to each other in thermodynamics
3. work (W)
2. heat (Q)
1. internal energy (U)
not all three are involed in every thermodynamic process
No work is done in a constant volume process
Isovolumetric Process ­ a thermodynamic process that takes place at constant volume so that no work is done on or by the system.
Example: bomb calorimeter
Isothermal Process ­ a thermodynamic process that takes place at constant temperature and in which the internal energy of a system remains unchanged.
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Section 11­1.notebook
February 28, 2012
Adiabatic Process ­ a thermodynamic process during which work is done on or by the system but no energy is transferred to or from the system as heat.
Example: filling a balloon quickly 6
Section 11­1.notebook
February 28, 2012
Practice 11A ­ all
Section Review ­ all
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