Chapter 17 THE FIRST LAW OF THERMODYNAMICS THERMODYNAMICS
- Slides: 29
Chapter 17 THE FIRST LAW OF THERMODYNAMICS
THERMODYNAMICS “A theory is the more impressive the greater the simplicity of its premises, the more different kinds of things it relates, and the more extended its area of applicability. Therefore the deep impression that classical thermodynamics made upon me. It is the only physical theory of universal content which I am convinced will never be overthrown, within the framework of applicability of its basic concepts. ” A. Einstein
(INTERNAL) ENERGY OF A GAS
CHANGE IN INTERNAL ENERGY ΔU An monatomic ideal gas moves from state A to state B along the straight line shown. In which case is the change in internal energy of the system the biggest? P(atm) 1. Case 1 2. Case 2 A B 4 4 3. Same A B 2 2 Case 1 3 9 V(m 3) Case 2 3 9 V(m 3)
SOLUTION P(atm) B 4 2 A Case 1 3 9 V(m 3) 4 A B 2 Case 2 3 9 V(m 3)
HEAT (REMINDER) Heat is the amount energy transfer due to a temperature difference. All other forms of energy transfer are classified as work. In the picture below, heat is flowing from the hot object to the cold object.
ENERGY TRANSFER (HEAT AND WORK) Q: Heat going into the system W: Work done by the system
WORK DONE ON OR BY THE SYSTEM HEAT INTO OR OUT OF THE SYSTEM (Work done by the system) = (− 1) × (Work done on the system) (Heat going into the system) = (− 1) × (Heat going out of the system) W = +100 J Work done by the system = +100 J Work done on the system = -100 J W = -150 J Work done by the system = -150 J Work done on the system = +150 J Q = +100 J Heat going into the system = +100 J Heat going out of the system = -100 J Q = -150 J Heat going into the system = -150 J Heat going out of the system = +150 J
THE FIRST LAW OF THERMODYNAMICS ΔU = Q - W Increase in internal energy Work done by system Heat going into system U, Q, W are all in J. When work done by the system is positive, the system loses energy. When work done by the system is negative, the system gains energy.
NOTATION IN SERWAY & JEWETT Our Notation W: work done by the gas U: internal energy ΔU=Q - W Serway’s Notation W: work done on the gas Eint: internal energy ΔEint=Q +W
EXAMPLES: ENERGY TRANSFER
WORK BY/ON A GAS
WORK DONE AND AREA UNDER THE CURVE
THE SIGN OF W If all the signs seems confusing, simply remember this: Expansion W >0 Compression W <0
W IS PATH-DEPENDENT The work in each case is different, so you must be careful when calculating W.
PATH DEPENDENCE OF W AND Q
EXAMPLE: WORK A system moves from state A to state B along the straight line shown. In which case is the work done by the system the biggest? 1. Case 1 P(atm) 2. Case 2 3. Same A B 4 4 2 A Case 1 3 B 2 9 V(m 3) Case 2 3 9 V(m 3)
SPECIAL CASES Isobaric: Isochoric: Isothermal: Adiabatic: constant pressure constant volume constant temperature no heat exchange Q =0 P P 1 W = PΔV 2 1 W=0 2 P PV = const 4 3 W V ΔV = 0 V V
SUMMARY
WORK FOR SPECIAL CASES
WORK FOR ISOTHERMAL CASE We used:
Imagine that an ideal monatomic gas is taken from its initial state A to state B by an isothermal process, from B to C by an isobaric process, and from C back to its initial state A by an isochoric process. Fill in the signs of Q, W, and ΔU for each step. P (atm) A 2 Step Q W ΔU A B + + 0 B C 1 B C A C 1 2 V (m 3) -- -- -- + 0 +
A CYCLIC PROCESS A process is cyclic if after one cycle the system returns to the starting point. For a cyclic process, after one complete cycle, ΔU=0, but Q and W may not be zero.
EXAMPLE: CYCLIC PROCESS W(A B) = W(C A) = − W(B C) = 0 W(A B C A) = = + 0 - = +12 k. J
HEAT CAPACITIES OF AN IDEAL GAS
RATIO OF HEAT CAPACITIES γ
ADIABATIC PROCESS Adiabatic processes obey the following relation:
EXAMPLE: ADIABATIC COMPRESSION A box of monatomic gas at pressure 1 atm is compressed from 6 m 3 to 2 m 3 adiabatically, adiabatically find the final pressure. What if the compression is isothermal but not adiabatic? adiabatic
W FOR ADIABATIC PROCESS By definition Q=0 for adiabatic processes. To find W, one can simply apply the First Law:
- Newton's first law and second law and third law
- Newton's first law
- First law of thermodynamics for open system
- Isobaric process formula
- 1th law of thermodynamics
- First law of thermodynamics joule's experiment
- Internal energy in thermodynamics definition
- Steady flow process thermodynamics
- First law of thermodynamics sign convention
- First law of thermodynamics control mass
- First law of thermodynamics
- First law of thermodynamics for ideal gas
- Boyle's law charles law avogadro's law
- Constant in avogadro's law
- Tatiana erukhimova
- Zeroth law example
- Newton's third law of thermodynamics
- Thermodynamics laws
- Formula for entropy change
- State second law of thermodynamics
- What is second law of thermodynamics
- Law of thermodynamics
- Second law of thermodynamics
- 2nd law of thermodynamics
- Thermodynamics enthalpy of reaction and hess's law
- Third law of thermodynamics is depend on
- Dq=cdt
- 1st law of thermodynamics
- 1st law of thermodynamics
- Zeroth law of thermodynamics