Thermodynamics Mock Test 2025 with Answers and Solutions

The First Law of Thermodynamics states that energy cannot be created or destroyed, only changed from one form to another. In mathematical terms, ΔU = Q - W, where ΔU is the change in internal energy of a system, Q is the heat supplied to the system, and W is the work done by the system. This law expresses the principle of conservation of energy for thermodynamic processes.

Common thermodynamic processes include:
• Isothermal process (temperature constant)
• Adiabatic process (no heat exchange)
• Isochoric process (volume constant)
• Isobaric process (pressure constant)
Each process has unique characteristics and is described by different forms of the gas laws and thermodynamic equations.

The Second Law of Thermodynamics states that in any natural thermodynamic process, the total entropy (a measure of disorder or randomness) of a system and its surroundings always increases or remains constant. This means that energy transformations are never 100% efficient and some energy is always lost as waste heat. This law explains why certain processes are irreversible, such as heat flowing from hot to cold bodies naturally.

An adiabatic process is one in which no heat is exchanged between the system and surroundings (Q = 0). During such a process, any work done leads to a change in the internal energy and temperature of the system. For example, the rapid compression or expansion of a gas in a piston, when insulated, is an adiabatic process.

The specific heat at constant pressure (Cp) is the amount of heat required to raise the temperature of one gram of a substance by 1°C at constant pressure, whereas the specific heat at constant volume (Cv) is the amount needed at constant volume. For gases, Cp is always greater than Cv because at constant pressure, some energy goes into doing work to expand the gas.

An isothermal process is a thermodynamic process in which the temperature remains constant throughout. For an ideal gas, this means internal energy does not change (ΔU = 0), so the heat supplied is entirely used to do work by the system or on the system. Such processes often occur slowly, allowing heat exchange with surroundings.

In thermodynamics, entropy (S) is a measure of the disorder or randomness in a system. It quantifies how much energy in a system is unavailable to do useful work. The Second Law states that entropy tends to increase in a closed system, signifying the natural tendency toward maximum disorder.

State functions are properties whose values depend only on the current state of the system, not on how the system reached that state. Examples include pressure, volume, temperature, internal energy, enthalpy, and entropy. They are essential for describing equilibrium properties in thermodynamics.

A reversible process is a hypothetical process that can be reversed at any point without leaving any change in either the system or the surroundings. An irreversible process occurs naturally and cannot be reversed because it involves the production of entropy and loss of useful energy (e.g., friction, spontaneous heat flow, mixing of gases).

To solve numerical problems using the First Law of Thermodynamics:
1. Write down what's given (heat supplied Q, work done W, change in internal energy ΔU).
2. Use the formula ΔU = Q - W.
3. Plug in the values with correct units.
4. Carefully interpret signs: Q is positive if heat enters system, negative if it leaves; W is positive if work is done by system, negative if work is done on system.
5. Calculate and check your units for consistency.

Thermodynamics is applied in various daily life and industrial processes such as:
• Refrigeration and air conditioning
• Working of automobile engines and turbines
• Design of power plants and boilers
• Steam generation and electricity production
• Understanding body temperature regulation and metabolic processes in humans