CHEM 101DL Lecture Notes - Lecture 4: Calorimetry

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chocolatecat618

20 Sep 2017

School

Duke University

Department

Chemistry

Course

CHEM 101DL

Professor

Christopher Roy, Mac Phail

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Document Summary

Speci c heat (s) - amount of heat required to raise 1 g of substance by 1 degree c. Heat capacity - amount of heat needed to raise the temperature of a given quantity of a substance by 1 degree c. Molar heat capacity - amount of heat needed to raise the temperature of 1 mol of a substance by 1 degree c q = m * c *t. A 466g sample of h2o(l) is heated from 8. 50 degrees c to 74. 6 degrees c. Calculate amount of heat absorbed q = m * s * t = (466)(4. 184)(74. 6-8. 50) = 1. 29 * 10^5 j. So we see that we get data on heats of reaction by direct methods (experiments), but since h is a state function, we are often interested in initial/ nal state. Turns out that we have tables of enthalpy of functions for substances. Hf for any element in its most stable state is 0.

Related Questions

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?

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.

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CHEM 101DL Lecture Notes - Lecture 4: Calorimetry

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