Chemistry name:
Heating Curve Problems 1
Date Given:
Heating/Cooling Curves A. The following graph is a heating curve showing the addition of heat at a constant rate of 500.0 joules/minute to a 3.00 gram sample of ice at –20.0°C. The final temperature of the vapor is 140.0°C.
Questions
1. During which segments is kinetic energy increasing? ______
2. During which segments does kinetic energy remain the same? ______
3. During which segments is potential energy increasing? ______
4. During which segments does potential energy remain the same? ______
5. During which segments is one phase only present? ______
6. During which segments are two phases present? ______
7. At what time does the liquid phase first appear? ______
8. At what time does the gas phase first appear? ______
9. At what time do the particles have the highest average kinetic energy? ______
10. Phase changes that occur with an absorption of energy are ______thermic.
11. ______(f______) and ______are endothermic phase changes.
12. During which segment could the heat of fusion be determined? ______
13. During which segment could the heat of vaporization be determined? ______
14. How long does it take to completely melt the sample at its melting point? ______
15. How long does it take to completely vaporize the sample at its boiling point?______
16. During which segment is the substance entirely in the solid state? ______
17. During which segment is the substance entirely in the gas state? ______
18. If 25.0 grams of ice at 0ºC are heated at a constant rate of 400.0 joules/minute, calculate the time needed to melt the sample completely. SHOW WORK.
19. If 25.0 grams of water at 100ºC are heated at a constant rate of 400.0 joules/minute, calculate the time needed to vaporize the sample completely. SHOW WORK.
20. Why is the time needed to vaporize the sample of water significantly greater than the time needed to melt the sample?
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B. The following is a cooling curve showing the release of heat at a constant rate of 500.0 joules/minute from a 3.00 gram sample of water vapor at 140.0°C. The final temperature of the ice is –20.0°C.
Questions
1. During which segments is kinetic energy decreasing? ______
2. During which segments does kinetic energy remain the same? ______
3. During which segments is potential energy decreasing? ______
4. During which segments does potential energy remain the same? ______
5. During which segments is one phase only present? ______
6. During which segments are two phases present? ______
7. At what time does the liquid phase first appear? ______
8. At what time does the solid phase first appear? ______
9. At what time do the particles have the highest average kinetic energy? ______
10. Phase changes that occur with a release of energy are ______.
11. ______and ______are exothermic phase changes.
12. During which segment could the heat of solidification be determined? ______
13. During which segment could the heat of condensation be determined? ______
14. How long does it take to completely freeze the sample at its freezing point? ______
15. How long does it take to completely condense the sample at its condensation point?____
16. During which segment is the substance entirely in the solid state? ______
17. During which segment is the substance entirely in the liquid state? ______
18. During which segment is the substance entirely in the gas state? ______
19. During which segment is there an equilibrium between the solid and liquid states? ______The temperature of the sample at this point is ______Kelvin.
20. During which segment is there an equilibrium between the liquid and gas states? ______The temperature of the sample at this point is ______Kelvin.
C. The following is a heating curve for substance X. 15.00 grams of substance X are heated at a constant rate of 500.0 joules/min.
For answers that require calculations, express using the correct number of significant figures and include units.
Time (minutes)
1. The melting point is ______. The boiling point is ______.
2. The time at which the liquid phase first appears is _____ minutes. The time at which the gas phase first appears is _____ minutes.
3. The sample is completely in the liquid phase between ______and ______minutes.
4. Determine the heat of fusion of this substance.
5. Determine the heat of vaporization of this substance.
6. Determine the specific heat of substance X ( in the liquid state).
7. Compare the intermolecular forces present in substance X to those present in a sample of water. Explain completely.
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Heating Curve of an Unknown Substance
Temperature
Heating Time
Identify the section or sections of the heating curve that satisfy the conditions described below. Use the letters A-E to identify the sections.
3. phase change occurs
4. melting occurs
5. substance exists as a solid and a liquid
6. vaporization occurs
7. substance has the highest density
8. kinetic energy is increasing (Temperature is used to measure average kinetic energy.)
9. potential energy is increasing
10. substance has no definite volume
11. The amount of heat energy that is necessary to convert matter from a solid to a liquid is called its heat of fusion, and is different for varying substances. The amount of heat energy that is necessary to convert matter from a liquid to a gas is called its heat of vaporization, and is different for varying substances. Does the substance have a higher heat of fusion or heat of vaporization? How do you know?
1. What happens to the temperature of this material during a phase change?
2. At what temperature does the gas condense?
3. At what temperature does the liquid boil?
4. What is the melting temperature of this substance?
5. At what temperature does the liquid freeze?
6. Does it take more energy to melt the solid or boil the liquid?
7. Does the solid give off energy or absorb energy when it melts? How much energy?
8. Once the liquid reaches the boiling point, how much energy must be added to make it boil?
9. Energy is released when a gas condenses. Where does this energy go?
10. Start at 20° C and then add 400 calories. What is the new phase? What is the new temperature?
11. If you keep adding heat to boiling water the temperature does not go up. What is the energy being used for??
Answer key
1. Temperature does not change!
2. 80° C
3. 80° C
4. 40° C
5. 40° C
6. Boiling takes more energy.
7. The solid absorbs 200 calories of energy.
8. 300 calories
9. The energy is dumped into the surrounding air.
10. It's the liquid phase, at approximately 65 ° C.
11. The energy is used to tear apart the liquid and turn it into gas.
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