THERMOCHEMISTRY REVIEW

You need a marker board, marker, eraser, & your Chemistry book.

What is the difference between kinetic and potential energy?

• Potential energy is stored energy (as in chemical bonds)

• Kinetic energy is the energy of motion (as in the motion of molecules)

What is the difference between temperature and heat.

• Heat is the total energy stored

• Temperature is the average kinetic energy of the molecules

Write the mathematical relationship between joules and calories.

• 1 calorie = 4.18 joules

Write the mathematical relationship between calories and kilocalories.

1000 calories = 1 kilocalorie

A banana has 110. nutritional calories. How many joules of

energy are in the banana?

• 4.60 x 105 joules

Endothermic reactions have ___________ H values

and exothermic reactions have ___________ H values

• Positive

• Negative

In an endothermic reaction the (system/surroundings) loses

energy and the (system/surroundings) gains

energy

• Surroundings

• System

Endothermic or Exothermic

• Ice Freezing• Dry Ice Subliming• Burning Marshmallow• Sweat Evaporating

• Exothermic• Endothermic• Exothermic• Endothermic

What is meant by specific heat?

• The amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius

Describe a calorimeter. What is it used for?

• A calorimeter is an insulated device, A calorimeter is an insulated device, such as a Styrofoam cup, used to such as a Styrofoam cup, used to measure the amount of heat absorbed measure the amount of heat absorbed or released during a chemical reaction.or released during a chemical reaction.

Use the table of specific heat values on page 492 of your text to

answer the following question.

The temperature of a sample of iron with a mass of 15.0 g changed from

25.5°C to 85.6°C. How many kilojoules of energy did this process take?

• q = (15.0)(0.449)(60.1) = 405 J = 0.405 kJ

Draw a heating curve for ammonia as it is warmed from -120°C to 300°C. The freezing point of

ammonia is -108°C and its boiling point is 270°C.

If 0.345 kJ of heat is released by 125 g water as it cools down from

85.2°C, what is it’s new temperature?

• 85.86ºC

If the heat of fusion for ammonia is 5.66 kJ/mol, how many kJ would be

required to melt 22.6 g of ammonia?

• 7.51 kJ

Using the following thermochemical equation: 2CO(g) + O2(g) 2CO2(g) ΔH = -566.0 kJ,

answer the following questions.

a. If 2.45 g of CO(g) reacts with sufficient oxygen gas, how many kJ of heat are released?

b. How many grams of carbon dioxide were produced when 234 kJ of heat were made?

• a. - 24.8 kJ

• b. 36.4 g CO2

Given the following data, determine the ΔH for the reaction:

2 Cu(s) + O2(g) 2 CuO(s)4CuO (s) 2Cu2O (s) + O2 (g)

ΔH = 288kJCu2O (s) Cu (s) + CuO (s)

ΔH = 11kJ

• -310 kJ (1st reaction flipped, 2nd flipped and doubled)

What is meant by the term “enthalpy?”

• Enthalpy (H) is the heat content of a system at a constant pressure

Explain how the Heat of Fusion and the Heat of Vaporization are

the same and different.

Which has more entropy, a sugar cube or a sugar solution?

• Sugar Solution

If a sugar cube dissolves in water, is the “S” for the reaction positive or negative?

Positive

Calculate the ΔG for this reaction at 298 K (room temperature ) and 1000K (very hot). Determine if each reaction is spontaneous.

O2 + O O3

ΔH = -106.5kJ ΔS = -127.4 J/K

Answer: at 298K ΔG=-68.5kJ so the reaction is spontaneousat 1000K ΔG=20.9 kJ so the reaction is not spontaneous