Download Template for calculating the ΔH° in a multiple step chemical reaction

Template for calculating the ΔH° in a multiple step chemical reaction...
QUESTION:
Calculate the Standard Enthalpy Δ for the reaction below...
Place chemical reaction here
ΔH°rxn = _______ kJ/mol
...given that...
1. ______________________________________
ΔH°rxn = _______ kJ/mol
2. ______________________________________
ΔH°rxn = _______ kJ/mol
3. ______________________________________
ΔH°rxn = _______ kJ/mol
I.
Before you begin, make sure all chemical equations are balanced.
II.
Rewrite the intermediary chemical equations so that they are in the correct order and make sure each
reaction is progressing in the same direction as the original equation stated in the question.
REWRITE
1. ______________________________________
ΔH°rxn = _______ kJ/mol
2. ______________________________________
ΔH°rxn = _______ kJ/mol
3. ______________________________________
ΔH°rxn = _______ kJ/mol
III.
Setup the formula for finding the total ΔEnthalpy in the formation of C2H6
(DO NOT FORGET TO ACCOUNT FOR EACH COMPOUND’S COEFFICIENTS)
ΔH°rxn (1) +
ΔH°rxn (2)
(
(
)______ +
+
ΔH°rxn (3) =
)_______ + (
total ΔH°
)_______ = _________
kJ/mol
PRACTICE PROBLEMS:
1. Calculate the Standard Enthalpy Δ for the reaction...
2 Al(s) + Fe2O2(s) → 2Fe(s) + Al2O3(s)
...given that...
1.
2.
2Al(s) + 3/2O2(g)
2Fe(s) + 3/2O2(g)
→
→
Al2O3(s)
Fe2O3(s)
ΔH°rxn = -1669.8kJ/mol
ΔH°rxn = -822.2 kJ/mol
total ΔH° =_________
Write the two steps in the proper order...
How to do it...
To make Al2O3, you need the O3 from Fe2O3. To do that, you must first carry out the process of breaking up the Fe2O3, which has its
own enthalpy of formation. However we are not forming Fe2O3. We are decomposing it. So, we must reverse the equation.
Fe2O3 → 2Fe(s) + 3/2 O2 (g)
Since the equation is reversed the enthalpy must be changed from -822.2 kJ/mol to 822.2 kJ/mol.
1). Fe2O3 → 2Fe(s) + 3/2 O2 (g) ΔH°rxn = 822.2 kJ/mol
Now, we can make Al2O3 from its component parts (Al and O2).
2). 2Al(s) + 3/2O2(g)
→ Al2O3(s) (the enthalpy of this step remains the same) ΔH°rxn = -1669.8kJ/mol
Add the enthalpy of the two steps together to get the total ΔH°rxn
822.2 kJ/mol + (-1669.8 kJ/mol) = -847 kJ/mol
2. Consider the following two reactions...
ΔH°rxn = ΔH1
A→2B
ΔH°rxn = ΔH2
A→C
Determine the enthalpy change for the process...
2B→C
The steps are 2B → A → C
You can leave the answer like this...
-ΔH1 + ΔH2
Additional Practice Problems
3.
From the following enthalpy changes,
H2 (g) + ½ O2 (g)  H2O (l)
H = 285.8 kJ
N2O5 (g) + H2O (l)

2 HNO3 (l)
H = 76.6 kJ
3
½ N2 (g)
+
/2 O2 (g) + ½ H2 (g)  HNO3 (l) H = 174.1 kJ
calculate the value of H for the reaction
2 N2 (g) + 5 O2 (g) 
2 N2O5 (g).
4.
From the following enthalpy changes,
CO (g) + SiO2 (s) 
SiO (g) + CO2 (g)
3 SiO2 (s) + 2 N2O (g) + 8 CO (g) 
8 CO2 (g) + Si3N4 (s)
calculate the value of H for the reaction
5 CO2 (g) + Si3N4 (s)  3 SiO (g) + 2 N2O (g)
+ 5 CO (g)
5.
H = +520.9 kJ
H = 461.1 kJ
From the following enthalpy changes,
H2 (g) + ½ O2 (g)  H2O (l)
H = 285.8 kJ
SO3 (g) + H2O (l)

H2SO4 (l)
H = 132.5 kJ
H2SO4 (l) + Ca (s)

CaSO4 (s) + H2 (g) H = 602.5 kJ
Ca (s) + ½ O2 (g)  CaO (s)
H = 634.9 kJ
calculate the value of H for the reaction
CaO (s) + SO3 (g) 
CaSO4 (s)
6.
Describe the difference between Heat Capacity and Specific Heat.
an example of each one.
Give
7.
Describe the difference between Heat of solution and Heat of dilution.
Give an example of each one.
8.
What is the molarity of a solution that contains 1.724 moles of H2SO4 in
2.50 L of solution?
9.
What is the molarity of a solution prepared by dissolving 25.0 g of HCl
(g) in enough water to make 150.0 mL of solution?
10.
Given the equation: 2Ag2S(s) + 2H2O(l) → 4Ag(s) + 2H2S(g) + O2(g) ΔH
= +595.5kJ,
calculate ΔH for the following reaction.
Ag(s) + ½ H2S(g) + ¼ O2(g) → ½ Ag2S(s) + ½ H2O(l)
11.
A 1.75 g sample of acetic acid, CH3CO2H, was burned in oxygen in a
calorimeter. The calorimeter contained 925 g of water and had a heat
capacity of 2.53 kJ/°C. The temperature of the calorimeter and its
contents increased from 22.2 °C to 26.5 °C. What is the molar heat of
combustion of acetic acid?
12.
A 3.5 g sample of quinine, C6H4O2, was burned in a calorimeter with a
heat capacity of 3.43 kJ/°C and contained 1.2 kg of water. The
temperature of the calorimeter and water increased fromv19.0°C to
28.0°C.
a) What is the molar enthalpy of combustion of quinine?
b) What is the specific enthalpy of combustion of quinine?
13.
The combustion of 1.00 mol of glucose, C6H12O6, releases 2820 kJ of
heat. If 2.0 g of glucose is burned in a calorimeter containing 1.0 kg of
water, and the temperature increases by 3.5 °C, what is the heat capacity
of the calorimeter?
14.
How many molecules are there in 9.34 grams of water?
15.
How many grams do 4.30 x 10^21 molecules of UF6 weigh?
16. IDENTIFY THE REACTIONS
The chemical reaction:
2 H2O2 → 2 H2O + O2 is a
a. synthesis reaction
b. decomposition reaction
c. single displacement reaction
d. double displacement reaction
e. combustion reaction
The chemical reaction:
Zn + H2SO4 → ZnSO4 + H2 is a
a. synthesis reaction
b. decomposition reaction
c. single displacement reaction
d. double displacement reaction
e. combustion reaction
The chemical reaction:
AgNO3 + NaCl → AgCl + NaNO3 is a
a. synthesis reaction
b. decomposition reaction
c. single displacement reaction
d. double displacement reaction
e. combustion reaction
The chemical reaction:
C10H8 + 12 O2 → 10 CO2 + 4 H2O is a
a. synthesis reaction
b. decomposition reaction
c. single displacement reaction
d. double displacement reaction
e. combustion reaction
The chemical reaction:
8 Fe + S8 → 8 FeS is a
a. synthesis reaction
b. decomposition reaction
c. single displacement reaction
d. double displacement reaction
e. combustion reaction
17. These molecules contain one or more double bonds or triple bonds or rings.
a. C3H4
b. C2H4O
c. C2H4O2
d. CHN
18. Use the HONC 1234 rule to construct a structural formula for the following:
a. C2H7N
b. N2H4
c. C2H8N2
19. In your words, explain the Law of Conservation of Energy
20. _______________ systems can exchange energy and mass,
whereas ________________ systems allow the transfer of energy (heat)
but not mass.
21. What is the third type of system in Thermochemistry?
__________________
22. LIST three examples of an intensive property:
23. LIST three examples of an extensive property:
24. FROM PPT:
The combustion of thiophene, C4H4S(l), a compound used in the
manufacture of pharmaceuticals, produces carbon dioxide and sulfur
dioxide gases and liquid water. The enthalpy change in the combustion of
one mole of C4H4S(l) is -2523kJ. Use this information and data from
Table 6.4 (p.247) to establish ΔH°f for C4H4S(l).