Energy Unit Conversions
Hess's Law
Thermochemical Stoichiometry
Calorimetry
Specific Heat
100
What are the units we use in Chemistry with energy?
Joules = J
100
The standard enthalpy change for the following reaction is 188 kJ at 298 K.
- H2O2(l)
H2(g) + O2(g) ΔH° = 188 kJ
What is the standard enthalpy change for this reaction at 298 K?
- H2(g) + O2(g) H2O2(l)
ΔH° = -188 kJ
100
What does a "+" and a "-" indicate about a reaction when part of the overall energy change of the reaction?
"+" = Endothermic
"-" = Exothermic
100
What equation is used to determine the overall energy of the water in a calorimeter? What is the "master" equation used when you have both a system and surroundings?
qH2O = mcT
Qsystem + Qsurroundings = 0
100
What does the specific heat capacity of a substance indicate? (Think units)
Specific heat capacity is the amount of energy required to change the temperature of 1 gram of a substance by 1 degree Celsius.
200
How many Joules are in a calorie? What is the difference between a calorie and a Calorie?
4.184 J = 1 calorie
1000 calories (cal) = 1 Calorie or kcal
200
The standard enthalpy change for the following reaction is -385 kJ at 298 K.
- Mn(s) + 1/2 O2(g) MnO(s) ΔH° = -385 kJ
What is the standard enthalpy change for the reaction at 298 K?
- 2 MnO(s) 2 Mn(s) + O2(g)
ΔH° = + 770 kJ
200
When HCl(g) reacts with NH3(g) to form NH4Cl(s) , 176 kJ of energy are evolved for each mole of HCl(g) that reacts.
Write a balanced thermochemical equation for the reaction with an energy term in kJ as part of the equation. Note that the answer box for the energy term is case sensitive.
HCl(g) + NH3(g) 
NH4Cl(s) + 176 kJ
200
A student heats 61.40 grams of iron to 98.13 °C and then drops it into a cup containing 83.25 grams of water at 21.20 °C. She measures the final temperature to be 26.56 °C.
The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.54 J/°C.
Assuming that no heat is lost to the surroundings calculate the specific heat of iron.
CFe = 0.427 J/g*C
200
In the laboratory a student finds that it takes 71.1 Joules to increase the temperature of 13.5 grams of solid iodine from 23.0 to 36.2 degrees Celsius.
The specific heat of iodine calculated from her data is...
Csp = 0.399 J/g*C
300
Complete the table conversions
Row 1: 656 J, 157 cal, 0.656 kJ
Row 2: 791 J, 189 cal, 0.791 kJ
Row 3: 712 J, 170. cal, 0.712 kJ
300
Given the standard enthalpy changes for the following two reactions:
(1) 2C(s) + H2(g) = C2H2(g) ΔH° = 226.7 kJ
(2) 2C(s) + 2H2(g) = C2H4(g) ΔH° = 52.3 kJ
What is the standard enthalpy change for the following reaction?
(3) C2H2(g) + H2(g) = C2H4(g) ΔH° = ?
ΔH° = -174.4 kJ
300
When N2(g) reacts with O2(g) according to the following reaction, 82.1 kJ of energy are absorbed for each mole of N2(g) that reacts. Complete the following thermochemical equation.
2N2(g) + O2(g) = 2N2O(g) H = ?
H = 164 kJ (to reactants side)
300
Since the cup itself can absorb energy, a separate experiment is needed to determine the heat capacity of the calorimeter. This is known as calibrating the calorimeter and the value determined is called the calorimeter constant.
One way to do this is to use a common metal of known heat capacity. In the laboratory a student heats 96.39 grams of copper to 98.57 °C and then drops it into a cup containing 84.53 grams of water at 22.78 °C. She measures the final temperature to be 29.94 °C.
Using the accepted value for the specific heat of copper (0.385 J/g*C), calculate the calorimeter constant.
Ccal = 2.03 J/*C
300
In the laboratory a student finds that it takes 28.7 Joules to increase the temperature of 10.8 grams of solid tin from 24.0 to 37.5 degrees Celsius.
The specific heat of tin he has measured is ...
Csp = 0.197 J/g*C
400
Complete table conversions
Row 1: 656 J, 0.656 kJ, 0.157 kcal
Row 2: 639 J, 0.639 kJ, 0.153 kcal
Row 3: 854 J, 0.854 kJ, 0.204 kcal
400
Given the standard enthalpy changes for the following two reactions:
(1) Ni(s) + Cl2(g)NiCl2(s)...... ΔH° = -305.3 kJ
(2) Pb(s) + Cl2(g)PbCl2(s)......ΔH° = -359.4 kJ
what is the standard enthalpy change for the reaction:
(3) Ni(s) + PbCl2(s)NiCl2(s) + Pb(s) ΔH° = ?
ΔH° = 54.1 kJ
400
The reaction of methane with oxygen to form carbon dioxide and water proceeds as follows:
CH4(g) + O2(g) = CO2(g) + H2O(g)
When 4.03 grams of CH4(g) react with sufficient O2(g), 202 kJ of energy are evolved. What is the value of H for the chemical equation given?
H = -804 kJ
400
A 0.560-g sample of adipic acid (C6H10O4) is burned in a bomb calorimeter and the temperature increases from 25.00 °C to 27.20 °C. The calorimeter contains 1.02×103 g of water and the bomb has a heat capacity of 799 J/°C. The heat capacity of water is 4.184 J g-1°C-1. Based on this experiment, calculate ΔE for the combustion reaction per mole of adipic acid burned.
ΔE = -2.91 x 103 kJ/mol
400
A sample of solid iodine is heated with an electrical coil. If 74.1 Joules of energy are added to a 11.2 gram sample initially at 22.5°C, what is the final temperature of the iodine?
Tfinal = 38.0 *C
500
A list of the calorie content of foods indicates that a croissant contains 251 Calories. Express this value in kJ and in J.
The Joule (J) is the SI unit of energy.
1.05 x 106 J
1.05 x 103 kJ
500
Given the standard enthalpy changes for the following two reactions:
(1) 2Pb(s) + O2(g)2PbO(s)
H° = -434.6 kJ
(2) 2Hg(l) + O2(g)2HgO(s)H° = -181.6 kJ
what is the standard enthalpy change for the reaction:
(3) PbO(s) + Hg(l)Pb(s) + HgO(s) H° = ?
H° = 126.5 kJ
500
The following thermochemical equation is for the reaction of hydrogen chloride(g) with oxygen(g) to form H2O(g) and chlorine(g).
4HCl(g) + O2(g)
2H2O(g) + 2Cl2(g) 
H = -114 kJ
How many grams of HCl(g) would have to react to produce 9.35 kJ of energy?
12.0 grams HCl
500
When 1.16 g of calcium chloride (CaCl2) is dissolved in 117 g of water in a styrofoam calorimeter of negligible heat capacity, the temperature increases from 25.00 to 26.84 °C. Based on this observation, calculate q for the water and ΔH° for the process, assuming that the heat absorbed by the salt is negligible.
CaCl2(s) 
Ca2+(aq) + 2Cl- (aq)
The specific heat of water is 4.184 J °C-1 g-1.
ΔH° = -86.2 kJ
500
A sample of solid silver is heated with an electrical coil. If 47.1 Joules of energy are added to a 14.3 gram sample and the final temperature is 38.1°C, what is the initial temperature of the silver?
Tinitial = 24.2 *C