The standard molar enthalpy of formation of diborane, B₂H₁ (g), cannot be determined directly because the compound cannot be prepared by the reaction of boron and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured. 4 B(s) + 3 O₂(g) → 2 B₂O3(s) A, H = -2543.8 kJ/mol-rxn H₂(g) + 1/2O2(g) → H₂O(g) A, H = -241.8 kJ/mol-rxn B₂H6 (g) + 3 O₂(g) → B₂O3(g) + 3 H₂O(g) A,H° = -2032.9 kJ/mol-rxn a we will show how these equations can be added together to give the equation for the formation of B₂ H6 (g) from B(s) and H₂(g) in their standard states and determine the enthalpy of formation. The target reaction is 2 B(s) + 3 H₂(g) → B₂ H6 (g) Does Reaction 1 need to be used as is, or reversed? as is reversed Correct The reaction is used as is because B(s) is a reactant in the target reaction and in Reaction 1. b Does Reaction 1 need to be multiplied by a scaler? Choose a scaling number for Reaction 1. Target Reaction: 2 B(s) + 3 H₂(g) → B₂H6 (g) Scaling number:
The standard molar enthalpy of formation of diborane, B₂H₁ (g), cannot be determined directly because the compound cannot be prepared by the reaction of boron and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured. 4 B(s) + 3 O₂(g) → 2 B₂O3(s) A, H = -2543.8 kJ/mol-rxn H₂(g) + 1/2O2(g) → H₂O(g) A, H = -241.8 kJ/mol-rxn B₂H6 (g) + 3 O₂(g) → B₂O3(g) + 3 H₂O(g) A,H° = -2032.9 kJ/mol-rxn a we will show how these equations can be added together to give the equation for the formation of B₂ H6 (g) from B(s) and H₂(g) in their standard states and determine the enthalpy of formation. The target reaction is 2 B(s) + 3 H₂(g) → B₂ H6 (g) Does Reaction 1 need to be used as is, or reversed? as is reversed Correct The reaction is used as is because B(s) is a reactant in the target reaction and in Reaction 1. b Does Reaction 1 need to be multiplied by a scaler? Choose a scaling number for Reaction 1. Target Reaction: 2 B(s) + 3 H₂(g) → B₂H6 (g) Scaling number:
Chemistry & Chemical Reactivity
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ISBN:9781337399074
Author:John C. Kotz, Paul M. Treichel, John Townsend, David Treichel
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Chapter5: Principles Of Chemical Reactivity: Energy And Chemical Reactions
Section: Chapter Questions
Problem 81GQ: The standard molar enthalpy of formation of diborane, B2H6(g), cannot be determined directly because...
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Transcribed Image Text:The standard molar enthalpy of formation of diborane, B₂H₁ (g), cannot be determined directly because the compound cannot be prepared by the reaction of boron
and hydrogen. It can be calculated from other enthalpy changes, however. The following enthalpy changes can be measured.
4 B(s) + 3 O₂ (g) → 2 B₂O3 (s)
A₁H° = -2543.8 kJ/mol-rxn
H₂(g) + 1/2 O₂ (g) → H₂O(g)
A, H = -241.8 kJ/mol-rxn
B2 H6 (g) + 3 O2 (g) → B₂O3 (g) + 3 H₂O(g) A₁H° = −2032.9 kJ/mol-rxn
a we will show how these equations can be added together to give the equation for the formation of B₂ H6 (g) from B(s) and H₂(g) in their standard states and determine the
enthalpy of formation. The target reaction is
2 B(s) + 3 H₂(g) → B2H6 (g)
Does Reaction 1 need to be used as is, or reversed?
as is
reversed
The reaction is used as is because B(s) is a reactant in the target reaction and in Reaction 1.
Correct
b Does Reaction 1 need to be multiplied by a scaler? Choose a scaling number for Reaction 1.
Target Reaction:
2 B(s) + 3 H₂(g) → B2H6 (g)
Scaling number:
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