Test: Basic Thermodynamics terms - Chemistry MCQ

State functions are used to specify the state of a thermodynamic system. The state is described by measurable macroscopic particles like pressure, temperature, volume, amount, etc and the is P, V and T are called state variables.

An adiabatic system does not allow the exchange of heat between system and surroundings. Energy is transferred to the surrounding only through work Done. In the adiabatic process, the total energy is given as zero.

Let P is pressure and V is volume whereas Gamma is the ratio of specific heat capacity at constant pressure and volume. The relation between pressure and volume in an adiabatic process is given by PV^γ constant.

An open system allows the transfer of both mass and energy into the system from the surroundings. An example of an open system is the human body, we consume food, energy and excrete waste.

In an adiabatic process, the total energy is always zero. We have that ΔH = ΔU + W, as ΔH is zero, we get ΔU + W = 0; ΔU = -W. But as work is done on the system by observing no heat W becomes negative, so ΔU = -(-)W = W. Hence ΔU = W.

When a work is done or by the system, heat passes into out of the system and matter enters or leaves the system, there is a change in internal energy of the system. It is represented by the symbol “U”.

The total energy in an adiabatic process is zero, so internal energy is equal to the negative of the work done. Here work done is given by 50 kilojoules, so the internal energy is -50 kilojoules as the sum of internal energy and the work done should be zero.

The first law of thermodynamics is commonly stated as the law of conservation of energy that is energy can neither be created nor be destroyed, in other terms we can also say that the energy of an isolated system is constant.

An open system allows only energy transfer whereas an isolated system neither allows energy nor mass transfer through the system from the surroundings. Isolated and closed systems are not the same. So the above statement is false.

Energy of a substance is directly proportional to its temperature. As we know that heat energy of a substance is q = mcΔT. If the temperature increases slowly then the energy also increases slowly.