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    Can someone help me with this question:

    Hydrazine may be obtained from the reaction between ammonia and hydrogen peroxide.
    2NH3(g) + H2O2(l) → N2H4(l) + 2H2O(l) ∆rHo = −241.0 kJ mol−1
    Work out the standard enthalpy change for the decomposition of hydrazine to its elements.
    The standard enthalpy changes of formation in kJ mol−1 are:
    NH3: −46.1; H2O2: −187.8; H2O: −285.8

    Is 241 from reactants to products?
    Second bit -92.2 + -187.8? = -280
    Am I doing it right? Thanks in advance
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    (Original post by Super199)
    Can someone help me with this question:

    Hydrazine may be obtained from the reaction between ammonia and hydrogen peroxide.
    2NH3(g) + H2O2(l) → N2H4(l) + 2H2O(l) ∆rHo = −241.0 kJ mol−1
    Work out the standard enthalpy change for the decomposition of hydrazine to its elements.
    The standard enthalpy changes of formation in kJ mol−1 are:
    NH3: −46.1; H2O2: −187.8; H2O: −285.8

    Is 241 from reactants to products?
    Second bit -92.2 + -187.8? = -280
    Am I doing it right? Thanks in advance
    The equation enthalpy can be worked out from enthalpy of formation of products - enthalpy of formation of reactants

    [ΔHf(N2H4) + 2 * ΔHf(H2O)] - [2*ΔHf(NH3) + ΔHf(H2O2)] = -241kJ

    Substitute values and rearrange to find hydrazine
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    (Original post by charco)
    The equation enthalpy can be worked out from enthalpy of formation of products - enthalpy of formation of reactants

    [ΔHf(N2H4) + 2 * ΔHf(H2O)] - [2*ΔHf(NH3) + ΔHf(H2O2)] = -241kJ

    Substitute values and rearrange to find hydrazine
    Do I have to include all the negatives.
    As what I have done is:
    Hydrazine + 2(285.8)- (2x46.1 + 187.8)=241
    Hydrazine + 291.6=241
    Hydrazine = -50.6Kj mol-1
    Does the negative -241 just show that it is an exothermic reaction?
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    (Original post by Super199)
    Do I have to include all the negatives.
    As what I have done is:
    Hydrazine + 2(285.8)- (2x46.1 + 187.8)=241
    Hydrazine + 291.6=241
    Hydrazine = -50.6Kj mol-1
    Does the negative -241 just show that it is an exothermic reaction?
    you must include all the signs...
 
 
 
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