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CHM 113 Lecture Notes - Lecture 11: Calorimetry

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School
ASU
Department
Chemistry
Course
CHM 113
Professor
Cabirac

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Document Summary

Amount of heat required to raise 1 gram of a substance by 1 degree. Celsius: energy = (mass in grams)(specific heat)(change in temperature, molar heat capacity. Amount of heat that can be absorbed by 1 mole of a substance when temperature increases by 1 degree celsius: energy = (moles of substance)(molar heat capacity)(change in temperature) Hess"s law: estimate unknown change in enthalpy using known change in enthalpy values and the properties of enthalpy. If a reaction is carried out in several steps, the change in enthalpy for the whole reaction will be equal to the sum of enthalpy changes of each step. Standard enthalpies of formation = 0 for an element in its normal state. Wave nature of light: visible light is only a small part of the light spectrum, speed of light is 3. 0x108m/s, wavelength. Distance from peak to peak or trough to trough: frequency. Number of waves passing a given point per unit: speed of light = (wavelength)(frequency)

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Related Questions

1) What is the objective of this experiment? (Name of the experiment Introduction to Calorimetry)

A) To redefine Hess' Law.

B) To measure the light emitted from the reaction solution.

C) To measure the enthalpy of several acid-base reactions and to use these enthalpies along with Hess' law to determine the enthalpy of an acid base reaction not performed in the laboratory.

D)To study some of the properties of nable gases and thier reaction to acidic environments.

2) What is the SI unit for heat ?

A) Gallons.

B) Grams.

C) Moles.

D) Joules.

3) Which of the following has the units: J/gK?

A) Endothermic.
B) Specfic heat.
C) Enthalpy.
D) Heat capacity.

4) How would you define Specfic Heat (c)?

A) The amount of energy required to raise a mass one degree Celcius ( or Kelvin).

B) The change in temperature that occurs from one gram of substance releasing one Joule of energy.

C) The amount of heat required to raise one gram of a substance one degree Celcius (or Kelvin).

D) The amount of mass required to release one Joule of energy.

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

Part A

Find ΔErxn 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/∘C.

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/(mol⋠∘C). 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/(g⋠∘C). The heat capacity of a substance is therefore related to the energy q needed to raise its temperature by an amount ΔT. That is, q=nCpΔT, where n denotes the number of moles of the substance, or q=mCsΔT, 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 13.0∘C to 24.8 ∘C. 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/mol⋠∘C. How much energy would it take to raise the temperature of 9.90 g of silver by 16.0 ∘C?

Express your answer with the appropriate units.

Part 3

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

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/(mol⋠∘C). 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/(g⋠∘C).

The heat capacity of a substance is therefore related to the energy q needed to raise its temperature by an amount ΔT. That is, q=nCpΔT, where n denotes the number of moles of the substance, or q=mCsΔT, 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 13.0∘C to 24.3 ∘C. 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/mol⋠∘C. How much energy would it take to raise the temperature of 11.1 g of silver by 15.8 ∘C?

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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