Thermal Physics Questions Thomas Russell Question: State the first law of thermodynamics Answer: The heat added to a closed system equals the change in the internal energy of the system plus the work done by the system OWTTE Question: State two characteristics of an ideal gas Answer: Any two of the following - There are no intermolecular forces between the gas particles; There is no loss of collision when the molecules collide; Constant, rapid and random motion Question: What is the difference between an Isothermal process and an Adiabatic process? Answer: An Isothermal process is one in which the pressure and volume are varied and the temperature is constant in the system and an Adiabatic process is one in which no heat leaves or enters the system and hence Q=0. OWTTE Question: If 52J of work is done on a system and 364J of heat is added, determine the change of internal energy of the system Answer: 416J Question: State the second law of thermodynamics Answer: The total entropy of any system plus that of its environment increases as a result of all natural processes OWTTE Thermal Physics Questions Thomas Russell Topic 10 Thermal Physics 10.1 Thermodynamics 10.1.1 State the Equation of state for an ideal gas PV=nRT P=Pressure V=Volume n=Number of moles R=gas constant 8.31 J mol-1 K-1 T=Temperature (K) 10.1.2 Describe the difference between an ideal gas and a real gas An ideal gas contains no intermolecular forces, no kinetic energy is transferred through collisions and all particles move constantly, rapidly and in a random motion 10.1.3 Describe the concept of absolute zero and the Kelvin scale of temperature Absolute zero is the minimum temperature as it occurs at 0 pressure according to the Charles law. The Kelvin scale has the same scaling as the Celsius scale but is 273.15° lower 10.2 Processes 10.1.4 Solve problems using the equation of state of an ideal gas TIP: Just use this: PV=nRT 10.2.1 Deduce an expression for the work involved in a volume change of a gas at constant pressure 𝐹 𝑝= 𝐴 𝐹 = 𝑝𝐴 ∆𝑊 = 𝐹 × ∆𝑙 ∆𝑊 = 𝑝 × 𝐴 × ∆𝑙 ∆𝑊 = 𝑝 × ∆𝑉 10.2.5 Draw and annotate thermodynamic processes and cycles on a P-V diagram 10.2.2 State the first law of thermodynamics The heat added to a closed system equals the change in the internal energy of the system plus the work done by the system 𝑸 = ∆𝑼 + 𝑾 10.2.6 Calculate from a P-V diagram the work done in a thermodynamic cycle 10.2.3 Identify the first law of thermodynamics as a statement of the principle of energy conservation Within the equation, all energy transfers are identified and hence no energy is created or destroyed 10.2.7 Solve problems involving state changes of a gas 10.2.4 Describe the isochoric, isobaric, isothermal and adiabatic changes of state of an ideal gas IsochoricConstant volume IsobaricConstant Pressure IsothermalConstant Temperature Adiabatic- No heat flow in or out of system Thermal Physics Questions Thomas Russell 10.3 The second law of thermodynamics and entropy The Carnot engine 10.3.1 State that the second law of thermodynamics implies that thermal energy cannot spontaneously transfer from a region of low temperature to a region of high temperature The Kelvin-Planck statement of the 2nd LoT states that It is impossible for an engine working in a cycle to transform a given amount of heat from a reservoir completely into work. 10.3.2 State that entropy is a system property that expresses the degree of disorder in the system Entropy is a thermodynamic function and can be interpreted as the amount of order or disorder of a system. The change in entropy is more important than its absolute state If this is true, then it can be said that the opposite is true: 10.3.3 State the second law of thermodynamics in terms of entropy changes Clausius statement: It is impossible to make a cyclic engine whose only effect is to transfer thermal energy from a colder body to a hotter body The total entropy of any system plus that of its environment as a result of all natural processes ∆𝑆 = 𝑄 𝑇 10.3.4 Discuss example of natural processes in terms of entropy changes Note that while local entropy in a system may decrease, the entropy of the system will usually increase by a greater factor due to that process. Heat death of the universe- Degradation of all energy to a non-useful form A piece of ice can slide down an incline if the friction is overcome. In this process mechanical energy is converted into non-useful thermal energy through the friction process. Thermal Physics Questions Thomas Russell