Answers and Explanations

REVIEW QUESTIONS

1 . E

Boyle’s law states  that    when    a   gas is  held    at  constant    temperature,    its pressure    and volume  are

inversely   proportional.   This    means   that    as  the pressure    increases,  the volume  decreases,  and

vice    versa.  Of  the answer  choices,    the only    one that    involves    both    pressure    and volume—in

addition    to  a   controlled  variation   of  one of  the variables—is    choice  E.  When    a   balloon is  placed

in  a   bell    jar,    the volume  of  the balloon will    increase    as  a   vacuum  is  being   drawn   in  the jar.

Boyle’s law can be  used    to  predict this    behavior.

2 . C

This    question    is  an  application of  Charles’s   law,    which   states  that    at  constant    pressure,   the

volume  and temperature of  a   gas will    vary    in  direct  proportion  to  each    other.  If  a   50  L   volume

of  gas is  heated  from    standard    temperature,    which   is  273 K,  to  two times   standard

temperature,    576 K,  the volume  will    double  as  well.   Therefore,  the volume  of  the gas will

increase    from    50  L   to  100 L.

3 .  74

Using   the ideal   gas law,    we  can determine   the number  of  moles   of  the gas:

The molecular   weight, or  molar   mass,   of  the gas can then    be  found   by  dividing    the mass    of  the

gas by  the number  of  moles   it  contains:   2.5 g/0.034 mol =   74  g/mol.

4 . The conditions  that    define  an  ideal   gas are low pressure    and high    temperature.    Under   these

conditions, the ideal   gas assumption  that    gas molecules   have    no  intermolecular  forces  and

occupy  no  volume  is  most    valid.