Hot and Cold Pack Review Study Guide
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Name___ ___ ___ ___ Hour_ __ _ Hot and Cold Pack Unit Review 7.1 Endothermic and Exothermic ● Sy st em vs. Su rroun di ngs ● Endo th er mic Process ● Ex ot hermic Pr oc ess ○ Wha t is th e dif fere nce b etwe en ex othe rmic a nd en doth ermi c? ○ Is a hot p ack th e resu lt of an e xoth ermi c or end othe rmic p roce ss? Ho w do yo u know? ○ Are the follo win g en do- or exo thermic? ■ melting ice ■ boiling w ater ■ freezing water ■ dry ice turn ing into gas 7.2 Calorimetry and Heat Capacity ● Wha t are two way s ener gy cha nge s can oc cur during a physical chang e? ● Kno w the differ ence s and simil ariti es betwe en heat , energ y, entha lpy, and te mperature. ● Wha t are the Unit s for mea surin g en ergy ? (mo re th an o ne) ● Kno w wha t hea t cap acit y is and be able to do ca lculations. ○ How ma ny jo ules are needed to warm 4 5.0g o f wate r from 1 5°C to 57°C ? ■ What f ormula d o y ou need? ○ If 458 c alories o f ener gy are a dded to 120.0 g of wat er at 25°C, what will the final temperature be? ● What is specif ic hea t capaci ty? ○ Be able to d efine thermal equil ibr ium ■ Two obj ects pl aced to gethe r at different temperatur es will come to thermal equilibrium- heat will flow until they are the same temperature. Would an object with a high specific heat capacity or one with a low specific heat capacity come to thermal equilibrium faster? ■ Expla in wh y, when you take clothe s that a re still d amp ou t of a c lot hes dryer, they don’t feel hot, but if you wait until ther’re dry to take the out, they feel quite hot. ● Calorimetry ○ Know ∆Hmetal = -∆Hwater can be used as mmetal x Cp metal x ∆Tmetal= -mwater x Cp water x ∆Twater for before and after conditions Calorimetry Practice:
Transcript of Hot and Cold Pack Review Study Guide
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Name________________________ Hour___________
Hot and Cold Pack Unit Review
7.1 Endothermic and Exothermic
● System vs. Surroundings● Endothermic Process● Exothermic Process
○ What is the difference between exothermic and endothermic?○ Is a hot pack the result of an exothermic or endothermic process? How do you
know?
○ Are the following endo- or exothermic?
■ melting ice
■ boiling water
■ freezing water
■ dry ice turning into gas
7.2 Calorimetry and Heat Capacity
● What are two ways energy changes can occur during a physical change?
● Know the differences and similarities between heat, energy, enthalpy, and temperature.
● What are the Units for measuring energy? (more than one)
● Know what heat capacity is and be able to do calculations.
○ How many joules are needed to warm 45.0g of water from 15°C to 57°C?
■ What formula do you need?
○ If 458 calories of energy are added to 120.0g of water at 25°C, what will the final
temperature be?
● What is specific heat capacity?
○ Be able to define thermal equilibrium
■ Two objects placed together at different temperatures will come to
thermal equilibrium- heat will flow until they are the same temperature.
Would an object with a high specific heat capacity or one with a low
specific heat capacity come to thermal equilibrium faster?
■ Explain why, when you take clothes that are still damp out of a clothes
dryer, they don’t feel hot, but if you wait until ther’re dry to take the out,
they feel quite hot.
● Calorimetry
○ Know ∆Hmetal = -∆Hwater can be used as
mmetal x Cp metal x ∆Tmetal= -mwater x Cp water x ∆Twater for before and after conditions
Calorimetry Practice:
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1. A hot pack with a mass of 25.0g and a temperature of 95°C is added to a 150.0g sample of
water at 25°C. The final temperature of the system is 75°C. What is the specific heat capacity of
the hot pack? Find your answer in calories and Joules.
2. If a hot pack has a mass of 30.0 g and it is heated to a temperature of 85°C, what is the heat
capacity of the pack if it can warm 500.0g of water from 25°C to 40°C?
Find your answer in cal/g°C and J/g°C.
3. A 50.0g block of unknown substance at 70°C is placed in 73g of water at 16°C. The final
temperature of the system is 23°C. Find the specific heat capacity of the substance.
4. Determine the specific heat capacity of an unknown substance if the 47.5g block of the
substance at 78.9°C is placed in 78.5g of water at 8.20°C and the final temperature of the block
is 23.6°C.
7.3 Changes in State
● Know that temperature does not change during change in state.○ When an ice cube melts is it absorbing or giving off energy?
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○ What about when a liquid freezes, is energy being given off or absorbed?■ Talk about what is going on at the molecular level.
● Be able to explain why the temperature does not change during a phase change, but
does when a substance is in one state.
● Enthalpy changes during change in state include:
○ Melting and freezing
■ What is enthalpy of fusion?
■ ∆H= m x Hfusion
■ What units do you use?
■ Is the enthalpy change positive or negative if the substance is being
frozen?
● Boiling and condensation
○ What is enthalpy of vaporization?
■ ∆H= m x Hvaporization
■ What units do you use?■ Is the enthalpy change positive or negative if the substance is being
condensed?
● Look at the heating and cooling curves of water. Know what is happening at each stage,in terms of temperature, heat at the molecular level.
● You should know the specific heat of a substance is different at different states (solid,liquid, or gas).
● Also, when solving Change in State problems you will need to use different equations,
depending on whether the substance is freezing/melting or boiling/vaporizing and/or
whether there is a temperature change.
○ ∆H= m x Hfusion
○ ∆H= m x Hvaporization
○ ∆H= m x Cp x ∆T
● Explain the difference between heat capacity, heat of fusion, and heat of vaporization.○ Be able to explain/define them.
Changes in State Practice
1. How many calories are needed to warm 15.0g of water from -20°C to steam at 135°C? Thespecific heat of ice is 0.51 cal/g°C. The specific heat of steam is 0.48 cal/g°C. The heat of vaporization of water is 547.2 cal/g°C, and the heat of fusion of is is 80.87 cal/g.
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2. How many calories does it take to melt 3.0g of sodium chloride if the heat of fusion is
397.32 kcal/g?
3. How many would be required to vaporize 100.0 g of Freon if the enthalpy of vaporization is
35.0 cal/g?
4. It takes 79.91 cal to melt 1.0 gram of unknown substance. What is the enthalpy of fusion of
the substance?
5. A cold pack filled with gel, with a mass of 15 g, is frozen. It’s placed in 1000.0 g of water at
50°C. When the ice pack is completely thawed, the water is at 22°C. What is the enthalpy of
fusion of the ice pack?
Additionally,
1. Know the Kinetic Molecular Theory.
2. Know what a phase change is and what the molecules are doing in solid, liquid, or gas phase.
3. Know what the phase change curve of water looks like. Be able to explain what is
happening in terms of thermal energy, phase change energy, and chemical energy at each
part. (hint: think energy bar graphs)
4. Review worksheets on energy bar graphs.
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5. Review journal questions and concepts.
6. What is the difference between endothermic and exothermic reactions?
7. What does ∆H mean?
8. Define heat, temperature, and enthalpy. Know the difference between them.
9. List 3 ways energy can be transferred.
10. Know the different units used for energy.
