1.
A piece of stainless steel weighing 1.55 g absorbs 141 J of heat energy when its
temperature increases by 178oC. What is the specific heat of stainless steel?
q = m C Δ T so C = q
.
=
141 J .
= 0.511 J
o
mΔT
1.55 g (178 C)
g oC
2.
The specific heat of olive oil is 2.0 J/g oC. When 435 J of heat is added to the olive
oil in a pan the temperature increases from 25oC to 110oC. What amount (mass) of
olive oil was placed into the saucepan?
q=mCΔT
so m = q
.
=
435 J
.
= 2.6 g the unit g is in the
o
CΔT
2.0 J (85 C)
denominator of the
g oC
denominator so it
is really in the numerator.
3.
How many kilojoules (kJ) of heat are absorbed when 0.46 g of chloromethane
(C4H5Cl, boiling point 12.3oC) vaporizes at its boiling point? Chloromethane, ∆Hvap =
26.4 kJ/mol. Change the liquid to gas/vapor, use the Hvap number
q = m Hvap
4.
5.
q = (0.46 g) • (26.4 kJ) x ( 1 mol ) = 0.14 kJ
mol
88.5 g
How much energy in Calories (Cal) is needed to raise the temperature 49.32 g of
copper metal from 23.0oC to 137.0oC?
q = m C Δ T so q = 49.32 g x 0.385 J x 114.0oC x 1 cal = 517 Cal
g oC
4.18 J
What amount of energy is require to 40.0 grams of liquid water at room
temperature (23.0oC) and change it into 40.0 g of steam at 145.0oC?
Formula q = m C Δ T
and q = m H?? and need values for . . .
specific heat(C) Cice= 2.01 J/goC
Cliquid= 4.18 J/goC
C steam= 2.01 J/goC
and the phase heats (H)
Hfus= 6.02 kJ/mol
Hvap=40.7 kJ/mol
Starting with the T = 23.0oC the water is liquid need to use the Cliquid = 4.18 J/goC,
to change it to liquid water at 100.0oC (Δ T = 77.0oC).
q = (40.0 g) • (4.18 J) • (77.0oC) x ( 1 kJ ) = 12.9 kJ
g oC
1000 J
Change the liquid water to steam (gas), use the Hvap number
q = m Hvap
q = (40.0 g) • (40.7 kJ) x ( 1 mol ) =
90.4 kJ
mol
18.0 g
Now gas at a T = 100.0oC and need to use the Csteam = 1.67 J/goC, to change it to
steam at 145oC (Δ T = 45.0oC).
q= mCΔT
q = (40.0 g) • (2.01 J) • (45.0oC) x ( 1 kJ ) = 3.6kJ
g oC
1000 J
To determine the total energy the values need to be added together:
12.9 kJ +
90.4 kJ + 3.6 kJ = 106.9 kJ need correct sig figs and unit
q= mCΔT