CHEM 14B Lecture 2: Chemistry 14B Lecture 2 Notes

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redclam353

11 Feb 2017

School

UCLA

Department

Chemistry and Biochemistry

Course

CHEM 14B

Professor

Lavelle Laurence

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Document Summary

Heat required to raise temperature of object by 1 o c is called heat capacity. Depends on amount of substance, is extensive capacity. Dividing heat capacity by amount of substance present (rams) gives us specific heat capacity, an intensive property which does not depend on amount. (units: kj/ o c g) (units: j/k mol) Specific heat capacity is heat required to raise temperature of 1g by 1 o c. Molar heat capacity: heat required to raise temperature of 1 mole by 1 o c. C v = molar heat capacity of gas at constant volume. C p = molar heat capacity of gas at constant pressure. Heat required to heat gas at constant pressure: (q p ) = triangle h = n x c p x. Specific heat capacity often called specific heat, measured using calorimeter. Constant p calorimetry gives enthalpy values, constant v calorimetry uses a bomb calorimeter. change in temperature (units will be j)

Related Questions

When 0.595 g of biphenyl (C12H10) undergoes combustion in a bomb calorimeter, the temperature rises from 25.4 âC to 29.9 âC.

Part A

Find ÎErxn for the combustion of biphenyl in kJ/mol biphenyl. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.86 kJ/âC.

Part B

Learning Goal: To understand the concepts of heat capacity, specific heat, and molar heat capacity. Heat capacity, C, is the amount of energy required to raise the temperature of a substance by exactly 1 degree Celsius. The energy needed to warm an object increases as the mass of that object increases. We see this in our everyday life. For example, we know that it takes much more energy to heat a large tank of water than a small cup. Because of this dependence on mass, experimentally determined heat capacities are always reported in terms of the amount of the substance that is heated. One method is to report how much energy it takes to raise the temperature of one mole of a substance by exactly 1 degree Celsius. This value is the molar heat capacity, which has the symbol Cp.The molar heat capacity is given in the units J/(molâ âC). A second method is to report how much energy it takes to raise the temperature of one gram of a substance by exactly 1 degree Celsius. This value is the specific heat, which has been given the symbol Cs. The units for specific heat are J/(gâ âC). The heat capacity of a substance is therefore related to the energy q needed to raise its temperature by an amount ÎT. That is, q=nCpÎT, where n denotes the number of moles of the substance, or q=mCsÎT, where m denotes the number of grams of the substance.

Part 1

It takes 55.0 J to raise the temperature of an 9.90 g piece of unknown metal from 13.0âC to 24.8 âC. What is the specific heat for the metal?

Express your answer with the appropriate units.

Part 2

The molar heat capacity of silver is 25.35 J/molâ âC. How much energy would it take to raise the temperature of 9.90 g of silver by 16.0 âC?

Express your answer with the appropriate units.

Part 3

What is the specific heat of silver? Express your answer with the appropriate units.

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Heat Capacity

Learning Goal:

To understand the concepts of heat capacity, specific heat, and molar heat capacity.

Heat capacity, C, is the amount of energy required to raise the temperature of a substance by exactly 1 degree Celsius. The energy needed to warm an object increases as the mass of that object increases. We see this in our everyday life. For example, we know that it takes much more energy to heat a large tank of water than a small cup. Because of this dependence on mass, experimentally determined heat capacities are always reported in terms of the amount of the substance that is heated. One method is to report how much energy it takes to raise the temperature of one mole of a substance by exactly 1 degree Celsius. This value is the molar heat capacity, which has the symbol Cp.The molar heat capacity is given in the units J/(molâ âC). A second method is to report how much energy it takes to raise the temperature of one gram of a substance by exactly 1 degree Celsius. This value is the specific heat, which has been given the symbol Cs. The units for specific heat are J/(gâ âC).

The heat capacity of a substance is therefore related to the energy q needed to raise its temperature by an amount ÎT. That is, q=nCpÎT, where n denotes the number of moles of the substance, or q=mCsÎT, where m denotes the number of grams of the substance.

Part A

It takes 51.0 J to raise the temperature of an 11.1 g piece of unknown metal from 13.0âC to 24.3 âC. What is the specific heat for the metal?

Express your answer with the appropriate units.

Cs =

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Parts B and C

The next two questions pertain to silver. They have nothing to do with unknown metal described in Part A.

Part B

The molar heat capacity of silver is 25.35 J/molâ âC. How much energy would it take to raise the temperature of 11.1 g of silver by 15.8 âC?

Express your answer with the appropriate units.

q =

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Part C

What is the specific heat of silver?

Express your answer with the appropriate units.

SubmitHintsMy AnswersGive UpReview Part

To understand the concepts of heat capacity, specific heat, andmolar heat capacity.
Heat capacity, C, is the amount of energy required to raise thetemperature of a substance by exactly 1 degree Celsius. The energyneeded to warm an object increases as the mass of that objectincreases. We see this in our everyday life. For example, we knowthat it takes much more energy to heat a large tank of water than asmall cup. Because of this dependence on mass, experimentallydetermined heat capacities are always reported in terms of theamount of the substance that is heated. One method is to report howmuch energy it takes to raise the temperature of one mole of asubstance by exactly 1 degree Celsuis. This value is the molar heatcapacity, which has the symbol C_p.The molar heat capacity is givenin the units \rm J / mol \cdot{}^\circ C. A second method is toreport how much energy it takes to raise the temperature of onegram of a substance by exactly 1 degree Celsius. This value is thespecific heat, which has been given the symbol C_s. The units forspecific heat are \rm J / g \cdot{} ^\circ C.

The heat capacity of a substance is therefore related to the energyq needed to raise its temperature by an amount Delta T. That is, q= nC_{\rm p}\Delta T, where n denotes the number of moles of thesubstance, or q = mC_{\rm s}\Delta T, where m denotes the number ofgrams of the substance.

Part A
It takes 53.0 J to raise the temperature of an 8.10 g piece ofunknown metal from 13.0 C to 24.0 C. What is the specific heat forthe metal?
Express your answer numerically, J/g*C

Part B
The molar heat capacity of silver is 25.35 j/mol*C. How much energywould it take to raise the temperature of 8.10 g of silver by 13.8C?

Part C
What is the specific heat of silver?

CHEM 14B Lecture 2: Chemistry 14B Lecture 2 Notes

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