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