Concept explainers
When boron hydrides burn in air, the reactions are very exothermic
- (a) Write a balanced equation for the combustion of B5H9(g) in air to give B2O3(s) and H2O(g).
- (b) Calculate the enthalpy of combustion for B5H9(g) (ΔfH° = 73.2 kJ/mol), and compare it with the enthalpy of combustion of B2H6 (−2038 kJ/mol). (The enthalpy of formation of B2O3(s) is −1271.9 kJ/mol.)
- (c) Compare the enthalpy of combustion of C2H6(g) with that of B2H6(g). Which transfers more energy as heat per gram?
(a)
Interpretation:
The balanced chemical equation for the combustion of
Concept introduction:
- Balanced chemical equation of a reaction is written according to law of conservation of mass.
- Stoichiometry of a chemical reaction is the relation between reactants and products of the reaction and it is represented by the coefficients used for the reactants and products involved in the chemical equation
Answer to Problem 45PS
The balanced chemical equation for the combustion of
Explanation of Solution
Boron hydride of the formula
The balanced chemical equation for the combustion of
(b)
Interpretation:
The enthalpy of combustion of
Concept introduction:
Enthalpy of reaction is the energy required or energy released when a chemical reaction occurs. If the process is endothermic then the energy is absorbed on the formation of the product. In such a case the sign of enthalpy change is positive. If the process is exothermic, then the energy is released on the formation of the product. In such a case the sign of enthalpy change is negative. In general, combustion reactions are exothermic in nature.
The standard enthalpy change is expressed as,
Answer to Problem 45PS
The
Explanation of Solution
The
Given:
Refer to Appendix L for the values of standard enthalpies.
The standard enthalpy of
The standard enthalpy of
The standard enthalpy of
The standard enthalpy of
The balanced reaction is,
The standard enthalpy change is expressed as,
Substitute the values,
The enthalpy of combustion of
Thus, the enthalpy of combustion of
(c)
Interpretation:
The enthalpy of combustion of
Concept introduction:
Enthalpy of reaction is the energy required or energy released when a chemical reaction occurs. If the process is endothermic then the energy is absorbed on the formation of the product. In such a case the sign of enthalpy change is positive. If the process is exothermic, then the energy is released on the formation of the product. In such a case the sign of enthalpy change is negative. In general, combustion reactions are exothermic in nature.
The standard enthalpy change is expressed as,
Answer to Problem 45PS
The enthalpy of combustion of
The enthalpy of combustion for
The enthalpy of combustion for
Explanation of Solution
The enthalpy of combustion of
Given:
Refer to Appendix L for the values of standard enthalpies.
The standard enthalpy of
The standard enthalpy of
The standard enthalpy of
The standard enthalpy of
The balanced chemical equation is,
The standard enthalpy change is expressed as,
Substitute the values,
The molar mass of
Thus, the enthalpy of combustion for
The molar mass of
Thus, the enthalpy of combustion for
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Chapter 21 Solutions
Chemistry & Chemical Reactivity
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