Chemical Thermodynamics - SS2 Chemistry Past Questions and Answers - page 1
Which of the following statements is true according to the First Law of Thermodynamics?
Energy can be created or destroyed.
The total energy of a closed system remains constant.
Energy flows spontaneously from a cooler object to a hotter object.
The entropy of a system always increases.
The Second Law of Thermodynamics states that:
Energy is conserved in all physical and chemical processes.
Heat always flows from a higher temperature object to a lower temperature object.
The entropy of a system approaches zero as its temperature approaches absolute zero.
It is impossible to construct a device that operates in a cycle and extracts heat from a single reservoir to produce work.
The Third Law of Thermodynamics states that:
Energy is conserved in all physical and chemical processes.
The entropy of a pure crystalline substance is zero at absolute zero temperature.
The total energy of a closed system remains constant.
The entropy of a system always increases.
The change in internal energy (ΔU) of a system is given by:
ΔU = q - w
ΔU = q + w
ΔU = q/T
ΔU = -q - w
The equation ΔS = qrev/T relates which of the following quantities?
Change in internal energy and temperature
Change in entropy and heat transfer
Change in entropy and work done
Change in temperature and heat transfer
Discuss two laws of thermodynamics. Explain the concepts and implications of both laws, and provide examples illustrating their application.
The laws of thermodynamics are fundamental principles that govern the behaviour and transformations of energy in physical and chemical systems. The three laws of thermodynamics are as follows:
1. First Law of Thermodynamics (Law of Energy Conservation): The first law states that energy cannot be created or destroyed in an isolated system. It can only change form or be transferred from one system to another. This law is also known as the law of energy conservation. Mathematically, it can be expressed as ΔU = Q - W, where ΔU is the change in internal energy of the system, Q is the heat added to the system, and W is the work done on the system.
Example: When a gas is compressed in a cylinder, work is done on the gas by the surroundings, and the internal energy of the gas increases. If heat is added to the system, the internal energy further increases, and if work is done by the system, the internal energy decreases.
2. Second Law of Thermodynamics (Law of Entropy): The second law of thermodynamics states that the entropy (a measure of the disorder or randomness) of an isolated system always increases or remains constant in a spontaneous process. This law implies that natural processes tend to move towards a state of greater disorder. It also introduces the concept of entropy as a measure of the system's energy dispersal or the number of microstates associated with a given macrostate.
Example: Heat spontaneously flows from a hot object to a cold object, resulting in an increase in the overall entropy of the system. A cup of hot coffee left in a room eventually cools down as heat is transferred to the surroundings.
Users' Answers & CommentsWhich of the following statements best describes enthalpy?
It represents the disorder or randomness of a system.
It measures the heat content of a system at constant pressure.
It determines the direction of a spontaneous reaction.
It quantifies the free energy change of a reaction.
The standard enthalpy change of a reaction is defined as:
The change in enthalpy of the reaction when reactants are in their standard states.
The enthalpy change of a reaction that occurs at standard temperature and pressure.
The difference in enthalpy between products and reactants of a reaction.
The enthalpy change of a reaction when one mole of a compound is formed from its elements in their standard states.
Which of the following is an example of an exothermic process?
Melting of ice cubes at room temperature.
Dissolution of an ionic compound in water.
Evaporation of water.
Boiling of water
Entropy is a measure of:
The heat content of a system.
The disorder or randomness of a system.
The enthalpy change of a reaction.
The free energy change of a reaction.