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CHEM 121 Lecture 12: Chapter 8 Full Version

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29 Nov 2016

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Heat is the transfer of thermal energy between two bodies that are at different temperatures. Thermal energy is kinetic energy associated with the random motion of atoms and molecules. Temperature is the measure of the thermal energy. Chemical energy is potential energy stored within the bonds of chemical substances. System: what is releasing or gaining energy in the reaction. Energy out of the system to surroundings: - sign (releasing energy = exothermic) Energy into the system from surroundings: + sign (using energy = endothermic) Internal energy change = e nal - e initial = e. T = t nal - t initial. Heat capacity= the amount of heat in joules that takes to raise the temperature one degree. Speci c heat capacity= how well they store heat. Q(heat in j) = t( c) x speci c heat (j/ c x g) x mass (g) Heat lost by chemicals in reaction = heat gained by water in calorimeter.

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Related Questions

it is relatively easy to change the temperature of a substance tha

1.According to the following thermochemical equation, if 31.1 g of NO2 is produced, how much heat is released at constant pressure?how much heat is released at constant pressure?

2NO(g) + O2(g) â 2NO2(g);ÎHÂ° = â114.4 kJ

Select one:

a. 114.4 kJ114.4 kJ

b. 1.183Ã103kJ

c. 2.365Ã103kJ

d. 38.7 kJ

e. 1.088Ã105kJ

2.CalculateâââÎUâââof a gas for a process in which the gas absorbs ââ12 J ââof heat and does ââ20 Jââ of work by expanding.

Select one:

a. 8 J

b. 32 J

c. -32 J

d. 0, because âÎU is a state function

e. -8 J

3.If q = +56 kJ for a certain process, that process

Select one:

a. requires a catalyst.

b. is exothermic.

c. occurs rapidly.

d. is endothermic.

e. cannot occur.

4.If q = 18 kJ and w = 15 kJ for a certain process, that process

Select one:

a. requires a catalyst.

b. has an increase in internal energy.

c. occurs slowly.

d. is exothermic.

e. cannot occur.

5.What is the change in internal energy of the system (ÎU) if 10 kJ of heat energy is released by the system and â70 kJâ of work is done on the system for a certain process?

Select one:

a. â60 kJ

b. 80 kJ

c. 10 kJ

d. 60 kJ

e. â80 kJ

6.What is the quantity of heat evolved at constant pressure when ââ26.3 gââ H2O(l)ââ is formed from the combustion of H2(g) and O2(g)?

2H2(g) + O2(g) â 2H2O(l);ÎHÂ° = â571.6 kJ

Select one:

a. 15033 kJ

b. 15.03 kJ

c. 1.72Ã104âkJ

d. 417.6 kJ

e. 9.57Ã102âkJ

7.What quantity, in moles, of hydrogen is consumed when 76.8 kJ of energy is evolved from the combustion of a mixture of H2(g) and O2(g)?

H2(g) + O2(g) â2H2O(l);ÎHÂ° = â571.6 kJ

Select one:

a. 2.368 mol

b. 1.184 mol

c. 0.4223 mol

d. 0.2687 mol

e. 1.368 mol

8. Which of the following is an exothermic process?

Select one:

a. work is done by the system on the surroundings

b. heat energy flows from the system to the surroundings

c. work is done on the system by the surroundings

d. heat energy is absorbed by the system

e. none of the above

9. Which of the following statements is correct?

Select one:

a. Internal energy is not a state function.

b. The value of q is negative when heat flows into a system from the surroundings.

c. The value of q is negative in an endothermic process.

d. Heat flows from a system into the surroundings in an exothermic process.

e. Enthalpy is not a state function.

10.X2and F2react according to the following equation, forming XF. (X is an unknown diatomic element)

X2(g)+ F2(g)â2XF(g);ÎHÂ°=+271 kJ

If X2(g) and F2(g) were mixed in a thermally insulated vessel, the reaction that occurred would be

Select one:

a. endothermic, and the temperature of the reaction system would fall.

b. We could not tell unless the original and final temperatures were given.

c. exothermic, and the temperature of the reaction system would fall.

d. exothermic, and the temperature of the reaction system would rise.

e. endothermic, and the temperature of the reaction system would rise.

1. What does a negative enthalpy value indicate about a chemical reaction?

1. Heat is required for the reaction and is located on the left of the reaction.

2. Heat is required for the reaction and is located on the right of the reaction.

3. Heat is released and is located on the left of the reaction.

4. Heat is released and is located on the right of the reaction.

2. 67 K is equivalent to:

is equivalent to:

4. Which of the following examples best represents heat?

1. A sample of platinum is

2. A piece of plastic contains 57 J of energy.

3. A piece of wood burns at

4. A toy car generates 45 J of kinetic energy.

5. Consider the combustion of propane

1. Is the combustion of propane endothermic or exothermic?

2. Is energy as heat released into the surroundings or absorbed by the system?

3. How much heat would this represent for the combustion of 3 moles of propane?

6. Calculate how much energy it takes to raise the temperature of 125 grams of aluminum from 100 to 245 degrees C. The specific heat of aluminum is 0.900 J/g degree C.

7. Calculate the heat change needed to raise the temperature of 1000 g of water from 5.0 degrees C to 95.0 degrees C.

8. How much energy is given off by the water in question number two if the 1000 g of water cools from 95.0 to 5.0 degrees C ?

9. Determine the specific heat of copper if it takes 10,500 J of energy to raise 520.0 grams of it from 27.0 degrees C to 245.0 degrees C

10. Determine the specific heat of an unknown element if it takes 540 J to raise the temperature of 55.6 grams of this element from 5.0 to 95.0 degrees C.