Heat Capacity Worksheet - Answer Key

 

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  1. What is molar heat capacity? 

    The energy required to raise the temperature of 1 mol of a substance by 1K.  Represented by, C.

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  2. What is specific heat capacity?

    The energy required to raise the temperature of 1 gram of a substance by 1K.  Represented by, C.

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  3. The kinetic energy of a system is directly related to its temperature.  So if we heat a system we increase its kinetic energy.

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  4. What are two conditions under which a gas can be heated?

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    • Constant Volume. 

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    • Constant Pressure. 

     

     

  5. What are the values for:

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    • Cv = 3/2 R

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    • Cp = Cv + R = 5/2 R

     

     

  6. Why is Cv<Cp?

    Cp > Cv because energy gets used for heating and work in constant pressure situation. 

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  7. When energy is added to a molecule there are three potential forms of motion that it can be transferred into:

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    • Translational – The molecule’s movement around the container
                                                                                                     
    • Vibrational – The spring-like movement of the bond between atoms.

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    • Rotational – The spinning of the molecule on an axis.

     

     

  8. Translational motion is the only motion that directly affects temperature.

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  9. The values 3/2 R and 5/2 R are only applicable to monatomic ideal gases. Why?

    A monatomic ideal gas is only capable of undergoing translational motion.

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  10. This means that the calculated molar heat capacities are often less than actual molar heat capacities.

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  11. What equation relates ΔE to heat capacity? 

    ΔE = nCVΔT

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    • Under what conditions can you use this equation?

      Under any all conditions. 

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    • Under what conditions does ΔE = q?

      When the volume is constant.

     

     

  12. What equation relates ΔH to heat capacity?

    ΔH = nCpΔT

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    • Under what conditions can you use this equation?

      Under any all conditions. 

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    • Under what conditions does ΔH=q?

      When the pressure is constant.

     

     

  13. Which value of R do we use in these equations?

    R = 8.3145 J mol-1K-1

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  14. Fill in the chart.

                 

     

     

  1. Consider a sample containing 5 moles of a monatomic ideal gas that is taken from State Aà State B by 2 different paths.  For each step, assume that the external P is constant and equals the final P of the gas for that step.  Calculate the values of q, w, ΔH and ΔE for each step along the 2 paths and the totals for the 2 paths.  What do the totals demonstrate?

    Path A:             q = 2.3 kJ                                 Path B:             q = 14.4 kJ
    w = 9.1 kJ                                                        w = – 3.04 kJ
    ΔE = 11.4 kJ                                                     ΔE = 11.4 kJ
    ΔH = 19.0 kJ                                                    ΔH = 19.0 kJ
                       

    The values of q and w are path dependent. 

     

    The values of ∆H and ∆E are path independent.

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