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3.1 Temperature and energy changes: Q = mL
3. Thermal physics
Steps
Worked example
Practice 1
Practice 2
Read the question carefully.
3.8 kg of a substance is heated
and absorbs 250 kJ of energy and
the whole amount evaporates.
Calculate the specifi c latent heat
of vaporisation. The substance
begins at its boiling point.
How much energy is required to
melt 2.5 kg of ice (L = 336 kJ
kg
-1
). The substance begins at its
meting temperature.
How much energy is required to
melt 0.8 kg of copper (L = 206 kJ
kg
-1
).
The substance begins at its
meting temperature.
Write what you know: highlight/
record the information from the
questions including what you
want to fi nd out.
Convert any data to appropriate
values (for example g to kg, or cm
to m)
Write down the equation that links
the variables together
Rearrange the equation to make
the unknown the subject
Substitute your data into the
equation, including the units
Calculate the answer, leaving a
unit and an appropriate number of
sig fi gs (same as data). Check
that the answer makes sense and
underline.
3.1 Temperature and energy changes: Q = mL
3. Thermal physics
Steps
Practice 3
Practice 4
Practice 5
:
write your own
Read the question carefully.
What is the specifi c latent heat of
fusion of a substance of 1.2 kg
when it melts by the addition of
135 kJ? The substance begins at
its meting temperature.
What is the specifi c latent heat of
fusion of a substance of 2.8 kg
when it melts by the addition of
0.9 kJ? The substance begins at
its meting temperature.
Write what you know: highlight/
record the information from the
questions including what you
want to fi nd out.
Convert any data to appropriate
values (for example g to kg, or cm
to m)
Write down the equation that links
the variables together
Rearrange the equation to make
the unknown the subject
Substitute your data into the
equation, including the units
Calculate the answer, leaving a
unit and an appropriate number of
sig fi gs (same as data). Check
that the answer makes sense and
underline.
3.1 Temperature and energy changes: Q = mL
3. Thermal physics
Steps
Worked example
Practice 1
Practice 2
Read the question carefully.
Write what you know: highlight/
record the information from the
questions including what you
want to fi nd out.
Convert any data to appropriate
values (for example g to kg, or cm
to m)
Write down the equation that links
the variables together
Rearrange the equation to make
the unknown the subject
Substitute your data into the
equation, including the units
Calculate the answer, leaving a
unit and an appropriate number of
sig fi gs (same as data). Check
that the answer makes sense and
underline.
3.1 Temperature and energy changes: Q = mL
3. Thermal physics
Steps
Practice 3
Practice 4
Practice 5
:
write your own
Read the question carefully.
Write what you know: highlight/
record the information from the
questions including what you
want to fi nd out.
Convert any data to appropriate
values (for example g to kg, or cm
to m)
Write down the equation that links
the variables together
Rearrange the equation to make
the unknown the subject
Substitute your data into the
equation, including the units
Calculate the answer, leaving a
unit and an appropriate number of
sig fi gs (same as data). Check
that the answer makes sense and
underline.
