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AQA A-level Chemistry Calculating Reaction Ξ”E

Calculating Reaction Ξ”E

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Bond enthalpies are measured for one mole of bonds in the gaseous state and are always endothermic. They can be used to measure energy change for a reaction by following these 3 steps.

Body energies

Energy change of reaction may need to be calculated to determine whether a reaction is exothermic or endothermic and sketch the reaction profile.

Reaction Profiles

1

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If the mean bond enthalpy of a Cβ€”O bond is +336 kJ/mol, what is the energy change when one mole of Cβ€”O bonds are made?

AQA A-level Chemistry Calculating Reaction Ξ”E If the mean bond enthalpy of a Cβ€”O bond is +336 kJ/mol, what is the energy change when one mole of Cβ€”O bonds are made?
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2

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Calculate Ξ”Hβ‚€α΅£ for this equation: 2NH₃(g) β†’ Nβ‚‚(g) + 3Hβ‚‚(g) where the mean bond enthalpies are: +391 kJ/mol (Nβ€”H), +945.4 kJ/mol (Nβ€”N), +435.9 kJ/mol (Hβ€”H).

AQA A-level Chemistry Calculating Reaction Ξ”E Calculate Ξ”Hβ‚€α΅£ for this equation: 2NH₃(g) β†’ Nβ‚‚(g) + 3Hβ‚‚(g) where the mean bond enthalpies are: +391 kJ/mol (Nβ€”H), +945.4 kJ/mol (Nβ€”N), +435.9 kJ/mol (Hβ€”H).
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3

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Sketch an endothermic reaction profile and indicate Ξ”H.

AQA A-level Chemistry Calculating Reaction Ξ”E Sketch an endothermic reaction profile and indicate Ξ”H.
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4

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Work out the energy change of this reaction: Hβ‚‚(g) + Clβ‚‚(g) β†’ 2HCl(g) given the bond enthalpies; Hβ€”H +436 kJ/mol, Clβ€”Cl +242 kJ/mol, H--Cl +431 kJ/mol. Is this an endothermic or an exothermic reaction?

AQA A-level Chemistry Calculating Reaction Ξ”E Work out the energy change of this reaction: Hβ‚‚(g) + Clβ‚‚(g) β†’ 2HCl(g) given the bond enthalpies; Hβ€”H +436 kJ/mol, Clβ€”Cl +242 kJ/mol, H--Cl +431 kJ/mol. Is this an endothermic or an exothermic reaction?
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5

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What information is needed to draw an accurate reaction profile diagram?

AQA A-level Chemistry Calculating Reaction Ξ”E What information is needed to draw an accurate reaction profile diagram?
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