Choose the correct statement.
Correct answer: A. The thermodynamics first law is not sufficient to predict the direction of the process
- A. The thermodynamics first law is not sufficient to predict the direction of the process
- B. In the case of an exothermic reaction, the overall enthalpy of the products is greater than that of reactants
- C. For the reaction H2(g) + Br2(l) → 2HBr (g) from the bond enthaly data, It is possible to calculate the value of H
- D. At 298K and 1 atmpressure, diamond's standard enthalpy is zero
Explanation
The first law of thermodynamics, which states that energy cannot be created or destroyed, but can be converted from one form to another, is not sufficient to predict the direction of a process. The first law only tells us that the total energy of a system and its surroundings remains constant, and does not provide any information about the entropy or disorder of the system. The direction of a process is determined by the second law of thermodynamics, which states that the total entropy of an isolated system always increases over time, or at best remains constant. Therefore, to predict the direction of a process, we need to consider both the first and second laws of thermodynamics. To predict the direction of the process, entropy and free energy change values are also used. The standard enthalpy of graphite is zero at 298K and 1 atm pressure and the standard enthalpy of a diamond is 1.8kJ/mol at 298K and 1 atm pressure. In the case of an exothermic reaction, the overall enthalpy of the products is lesser than that of reactants. An additional data of heat of vapourisation of Br2 (l) is also necessary for the calculation of H.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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