Enthalpy Worksheet

 

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  1. What is Enthalpy?  What is its symbol?

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  2. What is the equation for ΔH?

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  3. Under constant pressure circumstances what does ΔH equal?

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  4. Is enthalpy a state function?

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  5. Can enthalpy tell us whether a reaction is exothermic or endothermic?  If so, how?

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  6. For the following, predict the relationship between ΔE and ΔH for the following reactions at constant pressure:

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    • 2HF(g)→ H2 (g) + F2(g)

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    • N2(g) +3H2 (g)→ 2NH3 (g)

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    • 4NH3 (g) + 5O2 (g)→ 4NO(g) + 6H2O (g)

     

     

  7. Hess’ Law capitalizes on what property of enthalpy?

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  8. How do the following changes to a reaction affect ΔH values?

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    • Reverse of reaction →

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    • Multiplies reaction →

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    • Add up reactions →

     

     

  9. Given

    C6H4(OH)2 (aq)    → C6H4O2 (aq) + H2 (g)                     ΔH =177.4 kJ

     

    H2 (g) + O2 (g)     → H2O2 (aq)                             ΔH = -191.2 kJ

     

    H2 (g) + ½O2 (g)    → H2O (g)                                      ΔH = -241.8 kJ

     

    H2O (g)    → H2O (l)                                           ΔH = -43.8 kJ

    Determine ΔH for:

    C6H4(OH)2 (aq) + H2O2 (aq)    → C6H4O2(aq)+ 2H2O (l)

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  10. This symbol  ΔH°f represents ­­­­­­­­­­_________________. 

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  11. What is heat of formation?

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  12. What are the requirements to write out the heat of formation reaction equation for a molecule?

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  13. Which of the following represent a heat of formation reaction equation?
    If it is not correct, why?

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    • 6C(s) + 6H2O(l)→ C6H12O6 (s)

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    • Na(s) + Cl(g)→ NaCl(s)

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    • 2H2 (g) + O2(g)→ 2H2O(l)

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    • 1/2 N2 (g) +  3/2 H2 (g)→ NH3 (g)

     

     

  14. An element in its standard state has a ΔH°f equal to _______.  Why?

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  15. The equation to derive the ΔH°rxn from ΔH°f is

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  16. Calculate ΔH° rxn for the following:

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    • 4 Na(s)   +   O2 (g)   →   2 Na2O(s)

       

      ΔHfo = –416 kJ

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    • 2 Na(s)  +   2 H2O(l)     →  2NaOH(aq)   +   H2(g)

       

                         ΔHfo = –286 kJ         ΔHfo = –470 kJ           

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    • 2 Na(s)   +     CO2 (g)        →   Na2O(s)            +      CO(g)

       

      ΔHfo = –393.5 kJ      ΔHfo = –416 kJ       ΔHfo = –110.5 kJ

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