0th Law of Thermodynamics Consider 3 objects and their temperatures: T1 T2 T3 If T1 = T2 and T2 = T3 then T1 = T3

U W Q Walls can be either: Diathermal - heat can flow through Surroundings System U W Q Walls can be either: Diathermal - heat can flow through or Adiabatic – heat can’t flow through Car engine Q W Rub hands together W Q

The internal energy of an ideal gas depends only on its temperature The internal energy of an ideal gas depends only on its temperature. Therefore, the change in internal energy of a fixed amount of ideal gas (n moles) is given by: Units: Joules (J) R = 8.31 J/mol K

1st Law of Thermodynamics The total increase in the internal energy of a system is equal to the ‘sum’ of the work done on the system or by the system and the heat added to or removed from the system. (Conservation of Energy!) +ve Q = system GAINS heat (ΔU↑) -ve Q = system LOSES heat (ΔU↓) -ve W=work done BY system (ΔU↓) +ve W=work done ON system (ΔU ↑)

Pressure, Volume ,Temperature & Work In Thermodynamics we talk about the state of the system: Pressure, Volume ,Temperature & Work Work Done on a Gas F W = F Dx DV = A Dx W= PA Dx W = -P DV Dx Area +ve W=work done ON system (ΔU↑) COMPRESSION OF GAS DV -ve W=work done BY system (ΔU↓) EXPANSION OF GAS

Example: A gas is compressed from 1. 5 m3 to 1 Example: A gas is compressed from 1.5 m3 to 1.0 m3 under a constant pressure of 1.5 x 105 Pa while 3.0 x 105 J of heat is removed from the gas. What is the change in internal energy of the gas? Apply the first law. Heat is removed (system losses) Q = -3.0 x 105 J Work is performed [W +ve] on the gas; W = -pΔV = -(1.5 x 105Pa)(-0.5m3) = +0.75x 105J The change in internal energy: ΔU = -3.0 x 105 J + 0.75x 105J = 2.25x 105J System U W Q

During a thermodynamic process, 2,000 J of heat are removed from a gas while 600 J of work is done by the gas. What is the change in internal energy of the gas? (A) +2,600 J (B) 0 (C) -1,400 J (D) -2,600 J The internal energy of a sample of confined helium gas is increased by 300 J. If the net amount of work done on the sample by its surroundings was 240 J, how much heat was transferred between the gas and its environment? (A) 60 J absorbed (B) 540 J absorbed (C) 60 J dissipated (D) 540 J dissipated A gas undergoes an expansion in which 300 J of energy is added to the gas by heating. The internal energy of the gas changes from 600 J to 700 J. The work done by the gas is: (A) 1,300 J (B) 900 J (C) 200 J (D) 100 J

1. If 600 J of heat is added to a system as 200 Joules of work is done on the system, what is the change in its internal energy? 2. If 300 J of heat is added to a system as 300 joules of work is done by the system, what is the change in its internal energy? 3. Three moles of monatomic, ideal gas are in a rigid container. If the temperature is raised by 200 K while 5000 Joules of heat is added, find the work done on the gas and its change in internal energy? 3 moles

A Thermal Process… P V Po Pf Vo Vf 4.An ideal gas expands to 10 times its original volume, maintaining a constant 440 K temperature. If the gas does 3.3 kJ of work on its surroundings, how much heat does it absorb? T P V Po Pf Vo Vf In an isothermal process DU = 0 A Thermal Process…