CHEM 1033 Chapter Notes - Chapter 5: Heat Capacity, Thermal Energy

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25 Jul 2017

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Thermal energy is kinetic energy associated with the random motion of atoms and molecules. Temperature is a (cid:395)ua(cid:374)titati(cid:448)e (cid:373)easu(cid:396)e of (cid:862)hot(cid:863) o(cid:396) (cid:862)(cid:272)old. (cid:863) Heat (q) is the transfer of thermal energy between two bodies at different temperatures. Historically, energy was measured in units of calories (cal). A calorie is the amount of energy required to raise one gram of water by 1-degree c. the si unit of heat, work, and energy is the joule. A joule (j) is defined as the amount of energy used when a force of 1 newton moves an object 1 meter. We now introduce two concepts useful in describing heat flow and temperature change. The heat capacity (c) of a body of matter is the quantity of heat (q) it absorbs or releases when it experiences a te(cid:373)pe(cid:396)atu(cid:396)e (cid:272)ha(cid:374)ge (cid:894) t) of 1 degree celsius (or equivalently, 1 kelvin):

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.

Part B, C and D.

Question 2 Energy Calculations

a) Calculate the heat energy (q) when 12.0 g of water is heated from 20oC to 100oC. The

specific heat for water is given in your textbook.

b) Is the process of heating water exothermic or endothermic? Explain your answer.

Question 3 Energy Calculations

You dissolve 0.1 mol of ammonium nitrate in 100 mL of H2O. The temperature of the solution

changes from 22oC to 15oC. The specific heat capacity for water is 4.184 J/g.K. Show all

calculations on a separate sheet of paper!

a) Is this reaction endothermic or exothermic?

b) Calculate the heat, q, released or absorbed in the dissolution reaction.

c) Calculate the enthalpy change, ?Hrxn (kJ/mol), for dissolving 1 mol of ammonium nitrate.

Question 4. A gas expands from 264 mL to 971 mL at constant temperature. Calculate

the amount of work done in Joules by the gas when it expands against a constant pressure of 955

torr.

Question 5 Energy Calculations

a) The nutritional calorie (Calorie) is equivalent to 1 kcal. One pound (1.0 lb) of body fat is

equivalent to 4.1 x 103 kcal. Express this quantity in joules and kilojoules. Use

scientific notation for your answer!

b) If an athlete expends 1850 kJ/h (kilojoules per hour), how long does he have to exercise

to work off 1.0 lb of body fat?

c) The average amount of calories burned during running is 125 kcal/mile. How many

miles does this athlete have to run to burn off 1.0 lb of body fat?

Question 6

Calculate ?Ho for the following reactions at 298 K. Give the balanced thermochemical

equations and show the correct physical state in each equation. Calculate the enthalpy change

for each reaction. You will find thermochemical data in the back of your textbook in Appendix 3

(p. A-8 to A-12)

a) The formation of 1 mol of HCl (gas) from its elements

b) The formation of 1 mol of sodium chloride from its elements

c) The combustion of 1 mol glucose to water and carbon dioxide

d) HCl(g) + NH3(g) ? NH4Cl(g)

Question 7

Calculate heat of formation of SO2 under nonstandard state conditions, given the following

equations

SO2(g) +

CHEM 1033 Chapter Notes - Chapter 5: Heat Capacity, Thermal Energy

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