Thermodynamics
Relationships Between Heat and Work
Heat, Work, and Internal Energy
•As long as a substance does not change phase, its internal energy will ______as long as its temperature ______
•______can transfer energy to a substance
–Results in an increase in internal energy
•Can be transferred to another substance as ______
•Energy can be transferred to a substance as ______and from the substance as ____
•Heat and work are both ______transferred to or from a system
–______– a collection of matter within a clearly defined boundary across which no matter passes
–______– everything outside a system that can affect or be affected by the system’s behavior
•Also called the ______
•All the parts of a system are in thermal equilibrium with each other both before and after a process adds or removes energy
•Pressure is the force per unit area acting on an object
•Pressure = force / area
•P=F/A
•Measured in Pascal's = N/m2
–Other units are atmospheres (atm), millimeters of mercury (mmHg), bars (bar), pounds per square inch (psi), technical atmospheres (at), or torr (Torr)
•Caused by particle collisions
•Work done on or by a gas is the pressure multiplied by the change in volume
•Work = force * distance
•W=Fd
•W=pressure * volume change
•W=PΔV
•Change in volume = area * distance
•ΔV = Ad
•If the gas is compressed, ΔV is ______
•Work is done ______the system
•If the gas expands, ΔV is ______
•Work is done _____ the system
•If the volume remains constant, ______work is done
•An engine cylinder has a cross-sectional area of 0.010m2. How much work can be done by a gas in the cylinder if the gas exerts a constant pressure of 7.5*105 Pa on the piston and moves the piston a distance of 0.040 m?
•A = 0.010 m2d = 0.040m
•P = 7.5*105 Pa or 7.5*105 N/m2
•ΔV = ?W = ?
•ΔV=Ad = 0.010 m2 * 0.040 m = 4.0*10-4 m3
•W=PΔV = (7.5*105 N/m2) (4.0*10-4 m3) = 3.0*102 J
Thermodynamic Processes
•Work, internal energy, and heat are all ______
–Not every one of these is present in all ideal thermodynamic processes
•No work is done in constant-volume processes
–Called ______– a thermodynamic process that takes place at constant volume so that no work is done on or by the system
•Often take place in a bomb calorimeter
•Internal energy is constant in a constant-temperature process
•______process – a thermodynamic process that takes place at constant temperature and in which the internal energy of a system remains unchanged
–Similar to a balloon expanding as the pressure drops before a storm hits
•The balloon expands to keep pressure equal with the environment
•Energy is not transferred as heat during an ______process