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WorksheetsHeat and Thermodynamics
Total questions: 28
Worksheet time: 19mins
When and with what equation is Heat of Fusion used?
Q = mHf ; going between solids and liquids
Q = mHf ; going between liquids and gases
Q = mHv ; going between solids and liquids
Q = mHv ; going between liquids and gases
When and with what equation is Heat of Vaporization used?
Q = mHf ; going between solids and liquids
Q = mHf ; going between liquid and gases
Q = mHv ; going between solid and liquids
Q = mHv ; going between liquid and gases
In both Q=mC∆T and Q=mH , what does the m stand for
mass
heat
change in temperature
heat of fusion
heat of vaporization
In both Q=mC∆T and Q=mH , what does the Q stand for
mass
heat
change in temperature
heat of fusion
heat of vaporization
In both Q=mC∆T ; what does the ∆T (delta T) represent and how do you find it?
Change in Temperature = initial T - final T
Change in Temperature = final T - initial T
Initial Temperature
Final Temperature
When and with what equation is delta T (∆T or change in temperature) used?
Any SLOPED line in the phase change diagram ; Q=mC∆T
The FLAT line between solid and liquid; Q = mHf
The FLAT line between liquid and solid Q = mHv
If the questions asks about water freezing or melting, you should use...
Hf = 334 J/g
Hv = 2260 J/g
What will NOT be present in the question if you need to use heat of fusion or heat of vaporization
A value for Q (heat)
A value for m (mass)
A change in temperature (∆T)
The word boil
The word melt
Choose the correct formula for the problem: If 2083 Joules are used to MELT 5.26 grams of aluminum, what is the heat of fusion of aluminum
2083 J = (5.26 g) * Hv
2083 J = (5.26 g) * Hf
Q = (5.26 g) * (2083 J/g)
2083 J = (5.26 g) * -Hf
Choose the correct formula for the problem: If 5.26 grams of zinc is melted, and it takes 579 Joules to completely melt the sample. What is the
heat of fusion of zinc?
579 J = (5.26 g) * Hv
579 J = (5.26 g) * Hf
Q = (5.26 g) * (579 J/g)
cannot be determined
Choose the correct formula and answer for the question: How much energy does it take to boil a 125 g sample of water? (∆Hvap for water = 2260 J/g) (∆Hfus for water = 334 J/g)
Q = (125g) * (2260J/g) = 282,500 J
Q = (125g) * (344J/g) = 43,000 J
Q = (125g) / (2260J/g) = 0.055 J
Q = (125g) / (334J/g) = 0.374 J
Choose the correct formula and answer for: How much energy is released when a 175 g sample of ethanol condenses from the gaseous form to the liquid
form (Hvap for ethanol = -846 J/g)
Q = (175 g) * (-846 J/g) = -148,050 J
Q = (175 g) * (846 J/g) = 148,050 J
- 846 J/g = (175 g) * (Q) = -4.83 J
846 J/g = (175 g) * (Q) = 4.83 J
Why would a NEGATIVE Hvap be used in the question: How much energy is released when a 175 g sample of ethanol CONDENSES from the gaseous form to the liquid
form (Hvap for ethanol = -846 J/g)
Hv is negative because energy is RELEASED as gas molecules slow to the liquid state
Hv is negative because energy is ABSORBED as gas molecules slow to the liquid state
Hv is negative because energy is RELEASED as solid molecules slow to the liquid state
Hv should never be negative
Choose the correct formula and answer to the problem: What is the mass of a sample of Nickel, which completely melts after absorbing 3120 J of heat? (∆Hfus of nickel is 298 J/g)
Q = (m)(Hvap) ; m = 3120 / 298 = 10.5g
Q = (m)(Hfus); m = 3120 / 298 = 10.5g
Q = (m)(-Hfus); m = 298 / 3120 = 0.0955 g
Q = (m)(-Hfus); m = 298 / 3120 = 0.0955 g
In this problem, what is the key word and why is Hfus positive?? "What is the mass of a sample of Nickel, which completely melts after absorbing 3120 J of heat? (∆Hfus of nickel is 298 J/g)"
Key word = melts ; Hfus is positive because solid to liquid means molecules are ABSORBING energy
Key word = heat ; Hfus is positive because solid to liquid means molecules are ABSORBING energy
Key word = melts ; Hfus is positive because solid to liquid means molecules are RELEASING energy
Key word = heat ; Hfus is positive because solid to liquid means molecules are RELEASING energy
Choose the correct formula for the problem: How much energy is required to melt 7.84 g of ice
Q = (7.48g) * C * change in T
Q = (7.48g) * Hfus
Q = (7.48g) * Hvap
cannot be determined
Choose the correct formula for the problem: How much energy is required to cause 97.84 g of water to BOIL at 100C
Q = (97.48g) * C * 100C
Q = (97.48g) * Hfus
Q = (97.48g) * Hvap
Q = (97.48g) * -Hvap (note the negative sign)
Choose the correct formula for the problem: If 2083 Joules of energy are RELEASED to FREEZE 5.26 grams of aluminum, what is the heat of fusion of aluminum
2083 J = (5.26 g) * Hv
2083 J = (5.26 g) * Hf
Q = (5.26 g) * (2083 J/g)
-2083 J = (5.26 g) * Hf (note the negative sign)
Choose the correct formula for the problem: How much energy is released when 97.84 g of water vapor CONDENSES to a liquid at 100C
Q = (97.48g) * C * change in T
Q = (97.48g) * Hfus
Q = (97.48g) * Hvap
Q = (97.48g) * -Hvap (note the negative sign)
Why would a NEGATIVE Hf be used in the question: How much energy is RELEASED when a 175 g sample of liquid water FREEZES into ice
(Hvap for water = 334 J/g)
Hf is negative because energy is RELEASED as gas molecules slow to the liquid state
Hf is negative because energy is ABSORBED as solid molecules slow to the liquid state
Hf is negative because energy is RELEASED as liquid molecules slow to the solid state
Hf should never be negative
Q or heat is negative when energy is
released
absorbed
Q or heat is positive when energy is
released
absorbed
Why is a POSITIVE Hf used in this problem: How much energy is required to melt 7.84 g of ice (Hf = 334 J/g for water)
Change in temperature should be used instead of Hf
Hf should be negative since the sample is melting
Hf is positive because energy is being ABSORBED as the sample melts from a solid to a liquid
Hf is positive because energy is RELEASED as the sample melts from a solid to a liquid
Energy is ABSORBED going from a
solid to a liquid
liquid to a solid
liquid to a gas
gas to a liquid
Energy is RELEASED going from a
solid to a liquid
liquid to a solid
liquid to a gas
gas to a liquid
Since the ∆T = final T - initial T and Q=mC∆T , if the temperature of water increased from 4C to 80C as it was warmed on the stove, then...
∆T=80 - 4 = 76C and Q will be positive
∆T=80 - 4 = 76C and Q will be negative
∆T=4- 80 = -76C and Q will be negative
∆T=4- 80 = -76C and Q will be positive
Since the ∆T = final T - initial T and Q=mC∆T , if the temperature of water decreased from 75C to 25C as it cooled in the fridge, then...
∆T=75 - 25= 50C and Q will be positive
∆T=75 - 25 = 50C and Q will be negative
∆T=25 - 75 = -50C and Q will be negative
∆T= 25 - 75 = -50C and Q will be positive
If the questions asks about water condensing or vaporizing, you should use...
Hf = 334 J/g
Hv = 2260 J/g
