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Chemical Engineering Thermodynamics - Engineering

Q1:

Pick out the correct statement.

A If an insoluble gas is passed through a volatile liquid placed in a perfectly insulated container, the temperature of the liquid will increase.

B A process is irreversible as long as Δ S for the system is greater than zero.

C The mechanical work done by a system is always equal to P.dV.

D The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants.

ANS:D - The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants.

The correct statement is: "The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants." This statement accurately describes the concept of heat of formation, which represents the enthalpy change that occurs when one mole of a substance is formed from its elements in their standard states. The heat of formation of a compound refers to the amount of heat released or absorbed when one mole of the compound is formed from its constituent elements in their standard states. This concept is vital in understanding the energetics of chemical reactions and is often denoted by the symbol Δ𝐻𝑓ΔHf​. To explain the statement "The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants," let's break it down:

  1. Heat of reaction: This refers to the enthalpy change that occurs during a chemical reaction. It can be either exothermic (heat is released) or endothermic (heat is absorbed). In the context of forming a compound from its constituent elements, the heat of reaction specifically refers to the energy change associated with this process.
  2. Formation of the compound from its reactants: This part emphasizes that we are considering the formation of the compound from its individual elements. For example, the heat of formation of water (Δ𝐻𝑓ΔHf​ for H2OH2​O) would involve the reaction of hydrogen gas (H2H2​) and oxygen gas (O2O2​) to produce water (H2OH2​O).
So, when we say "The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants," we are essentially stating that the heat of formation quantifies the energy change associated with the formation of a compound from its constituent elements under standard conditions. This value helps chemists understand the stability and energy content of the compound, and it is often used in thermochemical calculations and the prediction of reaction outcomes.