Single Choice

Which of the following statements are correct?

AIf a certain process has an enthalpy change $$\Delta H$$, the reverse of that process has an enthalpy change of $$- \Delta H$$
BMultiplying a thermochemical equation by a constant also multiplies the thermodynamic quantity by that constant
CBoth $$A$$ and $$B$$
Correct Answer
DNone of these

Solution

Since $$H$$ is a state function, the standard enthalpy change of a forward process is the negative of its reverse. So if a certain process has an enthalpy change $$\triangle H$$, the reverse of that process has an enthalpy change of $$- \triangle H$$. A thermochemical equation is equation in molar quantities. Hence if both side of equations are multiplied by a factor to alter the number of moles, $$\triangle H,\triangle { H }°, \triangle { H }_{ f }$$ of the equation must be multiplied by the same factor since they are quantities per equation.

SIMILAR QUESTIONS

Chemical Thermodynamics

Regarding a thermochemical equation a wrong statement is

Chemical Thermodynamics

For the reactions, (i) $${H}_{2}(g)+{Cl}_{2}(g)=2HCl(g)+x$$ $$kJ$$ (ii) $$2HCl(g)={H}_{2}(g)+{Cl}_{2}(g)-y$$ $$kJ$$ which one of the following statements is correct?

Chemical Thermodynamics

$$C(s)\, +\, O_2(g)\, \rightarrow\, CO_2(g);\quad \Delta H\, =\, -\,94.3$$ kcal/mol $$CO(g)\, +\, 1/2\, O_2(g)\, \rightarrow\, CO_2(g);\quad\Delta H\, =\, -\,67.4$$ kcal/mol $$O_2(g)\, \rightarrow\, 2O(g);\quad \Delta H\, =\, 117.4$$ kcal/mol $$CO(g)\, \rightarrow\, C(g)\, +\, O(g);\quad \Delta H\, =\, 230.6$$ kcal/mol Calculate $$\Delta H$$ for $$C (s)$$ $$\rightarrow$$ $$C(g)$$ in Kcal/mol.

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