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# Calculate the Change in Enthalpy for the Reaction

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1- Calculate the change in enthalpy for the reaction. (Use 1.0g/mL as the density of the solution and 4.18J/g⋅ ∘ C as the specific heat capacity.)?

Instant cold packs, often used to ice athletic injuries on the field, contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken, the ammonium nitrate dissolves according to the following endothermic reaction:
NH 4 NO 3 (s)→NH 4 + (aq)+NO 3 − (aq)
In order to measure the enthalpy change for this reaction, 1.25 g of NH 4 NO 3 is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8 ∘ C and the final temperature (after the solid dissolves) is 21.9 ∘ C .

2- When 0.501g of biphenyl (C 12 H 10 ) undergoes combustion in a bomb calorimeter, the temperature rises from 25.2 ∘ C to 29.4 ∘ C. Find ΔE rxn for the combustion of biphenyl in kJ/mol biphenyl. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.86 kJ/ ∘ C .

3- What is the enthalpy for reaction 1 reversed? Express your answer numerically in kilojoules per mole. reaction 1 reversed: N 2 O 4 →N 2 + 2O 2

4- Calculate the enthalpy of the reaction

2NO(g)+O 2 (g)→2NO 2 (g) given the following reactions and enthalpies of formation:
1. 1/ 2 N 2 (g)+O 2 (g)→NO 2 (g), ΔH ∘ A =33.2 kJ
2. 1/ 2 N 2 (g)+ 1/ 2 O 2 (g)→NO(g), ΔH ∘ B =90.2 kJ
Express your answer with the appropriate units.
5- Calculate the enthalpy of the reaction
4B(s)+3O 2 (g)→2B 2 O 3 (s)
given the following pertinent information:
1. B 2 O 3 (s)+3H 2 O(g)→3O 2 (g)+B 2 H 6 (g), ΔH ∘ A =+2035 kJ
2. 2B(s)+3H 2 (g)→B 2 H 6 (g), ΔH ∘ B =+36 kJ
3. H 2 (g)+ 1 2 O 2 (g)→H 2 O(l), ΔH ∘ C =−285 kJ
4. H 2 O(l)→H 2 O(g), ΔH ∘ D =+44 kJ
Express your answer with the appropriate units.
6- Ozone, O 3 is destroyed when ClO levels are high. ClO is likely formed from the decomposition of chlorofluorocarbons (CFCs) in sunlight.
Standard enthalpies of formation for selected substances are given in the table below.
Substance ΔH ∘ f
(kJ/mol )

ClO(g)
101.0
ClO 2 (g)
102.0
O(g)
247.5
O 2 (g)
0
O 3 (g)
142.3
A- Calculate the standard enthalpy change of the reaction
ClO(g)+O 3 (g)→ClO 2 (g)+O 2 (g) Express your answer in kilojoules using four significant figures.
B- Calculate the standard enthalpy change of the reaction
ClO 2 (g)+O(g)→ClO(g)+O 2 (g) Express your answer in kilojoules using four significant figures.
C- Add the following reactions together:
ClO(g)+O 3 (g) ClO 2 (g)+O(g) → → ClO 2 (g)+O 2 (g) ClO(g)+O 2 (g) Identify which species cancel and which do not.

7- Consider the reaction N 2 (g)+3H 2 (g)→2NH 3 (g), ΔH =−92.3kJ
What will ΔH be for the reaction if it is reversed?
8- calculate the change in enthalpy for Reaction 2.
Reaction 1: C 3 H 8 (g)+5O 2 (g)→3CO 2 (g)+4H 2 O(g), ΔH 1 =−2043 kJ
Reaction 2: 4C 3 H 8 (g)+20O 2 (g)→12CO 2 (g)+16H 2 O(g), ΔH 2 =?
Express your answer to four significant figures and include the appropriate units.
9- calculate the reaction enthalpy, ΔH , for the following reaction:
CH 4 (g)+2O 2 (g)→CO 2 (g)+2H 2 O(l)
Use the series of reactions that follow:
1. C(s)+2H 2 (g)→CH 4 (g) , ΔH =−74.8 kJ .
2. C(s)+O 2 (g)→CO 2 (g) , ΔH =−393.5 kJ .
3. 2H 2 (g)+O 2 (g)→2H 2 O(g) , ΔH =−484.0 kJ .
4. H 2 O(l)→H 2 O(g), ΔH =44.0 kJ .
10- Calculate the standard enthalpy change for the reaction
2A+B⇌2C+2D
Use the following data:
Substance ΔH ∘ f
(kJ/mol)

A
-267
B
-383
C
191
D
-481
Express your answer to three significant figures and include the appropriate units.
11- What is ΔH ∘ rxnfor the following chemical reaction?
H 2 O(l)+CCl 4 (l)→COCl 2 (g)+2HCl(g)
You can use the following table of standard heats of formation (ΔH ∘ f ) to calculate the enthalpy of the given reaction.
Element/ Compound Standard Heat of Formation (kJ/mol) Element/ Compound Standard Heat of Formation (kJ/mol)
H(g)
218
N(g)
473

H 2 (g)
0
O 2 (g)
0

CCl 4 (l)
−139.5
O(g)
249

H 2 O(l)
−285.8
HCl(g)
−92.30kJ

C(g)
71
COCl 2 (g)
−218.8kJ

C(s)
0
HNO 3 (aq)
−206.6

Express the standard enthalpy of reaction to three significant figures and include the appropriate units.
12- The combustion of ethene, C 2 H 4 , occurs via the reaction
C 2 H 4 (g)+3O 2 (g)→2CO 2 (g)+2H 2 O(g)
with heat of formation values given by the following table:
Substance ΔH ∘ f
(kJ/mol)

C 2 H 4 (g)
52.47
CO 2 (g)
−393.5

H 2 O(g)
− 241.8

Calculate the enthalpy for the combustion of ethene.
Express your answer to four significant figures and include the appropriate units.

13- For which of the following reactions is ΔH ∘ rxn equal to ΔH ∘ f of the product(s)?
You do not need to look up any values to answer this question.
Check all that apply.
Check all that apply.

Na(s)+ 1 2 F 2 (l)→NaF(s)

2H 2 (g)+O 2 (g)→2H 2 O(g)

H 2 (g)+ 1 2 O 2 (g)→H 2 O(g)

H 2 O 2 (g)→ 1 2 O 2 (g)+H 2 O(g)

2Na(s)+F 2 (g)→2NaF(s)

Na(s)+ 1 2 F 2 (g)→NaF(s)

14- What is the balanced chemical equation for the reaction used to calculate ΔH ∘ f of BaCO 3 (s) ? If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation (s ), (l ), or (g ) for solid, liquid, or gas, respectively. Use (aq ) for aqueous solution.
Express your answer as a chemical equation

The standard enthalpy of formation (ΔH ∘ f ) is the enthalpy change that occurs when exactly 1 mol of a compound is formed from its constituent elements under standard conditions. The standard conditions are 1 atm pressure, a temperature of 25 ∘ C , and all the species present at a concentration of 1 M . A "standard enthalpies of formation table" containing ΔH ∘ f values might look something like this:
Substance ΔH ∘ f

H(g)
218 kJ/mol

H 2 (g)
0 kJ/mol

Ba(s)
0 kJ/mol

Ba 2+ (aq)
− 538.4 kJ/mol

C(g)
71 kJ/mol

C(s)
0 kJ/mol

N(g)
473 kJ/mol

O 2 (g)
0 kJ/mol

O(g)
249 kJ/mol

S 2 (g)
129 kJ/mol

15- nitrogen triiodide, NI 3 , and determine which of the following statements are correct.
Check all that apply.

NI 3 is a highly stable compound when it is dry.

In this reaction, heat is absorbed from the surroundings.

The enthalpy of NI 3 is greater than the enthalpy of the decomposition products.

In this reaction, iodine is produced as one of the products.

The decomposition of NI 3 is an exothermic reaction.

16- The decomposition of NI 3 to form N 2 and I 2 releases − 290.0 kJ of energy. The reaction can be represented as
2NI 3 (s)→N 2 (g)+3I 2 (g), ΔH rxn =−290.0 kJ
Find the change in enthaply when 19.0g of NI 3 decomposes.
Express your answer to three significant figures and include the appropriate units.
17-Consider the exothermic reaction
2C 2 H 6 (g)+7O 2 (g)→4CO 2 (g)+6H 2 O(g)
Calculate the standard heat of reaction, or ΔH ∘ rxn , for this reaction using the given data. Also consider that the standard enthalpy of the formation of elements in their pure form is considered to be zero.
Reactant or product ΔH ∘ f (kJ/mol)

C 2 H 6 (g)
-84.7
CO 2 (g)
-393.5
H 2 O(g)
-241.8
Express your answer to four significant figures and include the appropriate units.

17- Enthalpy H is a measure of the energy content of a system at constant pressure. Chemical reactions involve changes in enthalpy, ΔH which can be measured and calculated:ΔH rxn ∘ =∑ products mΔH f ∘ −∑ reactants nΔH f ∘ where the subscript "rxn" is for "enthalpy of reaction" and "f" is for "enthalpy of formation" and m and n represent the appropriate stoichiometric coefficients for each substance.The following table lists some enthalpy of formation values for selected substances.
Substance ΔH f ∘ (kJ/mol)

HCl(g)
−92

Al(OH) 3 (s)
−1277

H 2 O(l)
−285.8

AlCl 3 (s)
−705.6

H 2 O(g)
−241.8

a- Determine the enthalpy for this reaction:Al(OH) 3 (s)+3HCl(g)→AlCl 3 (s)+3H 2 O(l) Express your answer in kilojoules per mole to four significant figures.
b- Consider the reaction 2Al(OH) 3 (s)→Al 2 O 3 (s)+3H 2 O(l) with enthalpy of reaction
ΔH rxn ∘ =21.00kJ/mol. What is the enthalpy of formation of Al 2 O 3 (s)? Express your answer in kilojoules per mole to four significant figures.

18- Use the data below to answer the questions.
Substance ΔH ∘ f (kJ/mol)

C(g)
718.4
CF 4 (g)
− 679.9

CH 4 (g)
− 74.8

H(g)
217.94
HF(g)
− 268.61

Keep in mind that the enthalpy of formation of an element in its standard state is zero.
a- Suppose that 0.610mol of methane, CH 4 (g) is reacted with 0.760mol of fluorine, F 2 (g) , forming CF 4 (g) and HF(g) as sole products. Assuming that the reaction occurs at constant pressure, how much heat is released?Express your answer to three significant figures and include the appropriate units.

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The change in enthalpy for the reaction is calculated.

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1- Calculate the change in enthalpy for the reaction. (Use 1.0g/mL as the density of the solution and 4.18J/g⋅ ∘ C as the specific heat capacity.)?

Instant cold packs, often used to ice athletic injuries on the field, contain ammonium nitrate and water separated by a thin plastic divider. When the divider is broken, the ammonium nitrate dissolves according to the following endothermic reaction:
NH 4 NO 3 (s)→NH 4 + (aq)+NO 3 − (aq)
In order to measure the enthalpy change for this reaction, 1.25 g of NH 4 NO 3 is dissolved in enough water to make 25.0 mL of solution. The initial temperature is 25.8 ∘ C and the final temperature (after the solid dissolves) is 21.9 ∘ C .

Enthalpy change ΔH = mCΔT
ΔH = 25 g x 4.18 J/g oC x (21.9 - 25.8)oC = -407.55 J

2- When 0.501g of biphenyl (C 12 H 10 ) undergoes combustion in a bomb calorimeter, the temperature rises from 25.2 ∘ C to 29.4 ∘ C. Find ΔE rxn for the combustion of biphenyl in kJ/mol biphenyl. The heat capacity of the bomb calorimeter, determined in a separate experiment, is 5.86 kJ/ ∘ C .

ΔE rxn = 5.86 kJ/oC x (29.4 - 25.2)oC x (1 / 0.501g) x (154 g / 1 mol) = 7565 kJ/mol

3- What is the enthalpy for reaction 1 reversed? Express your answer numerically in kilojoules per mole. reaction 1 reversed: N 2 O 4 →N 2 + 2O 2 (Need data for this)

4- Calculate the enthalpy of the reaction

2NO(g)+O 2 (g)→2NO 2 (g) given the following reactions and enthalpies of formation:
1. 1/ 2 N 2 (g)+O 2 (g)→NO 2 (g), ΔH ∘ A =33.2 kJ
2. 1/ 2 N 2 (g)+ 1/ 2 O 2 (g)→NO(g), ΔH ∘ B =90.2 kJ
3. NO(g) → 1/ 2 N 2 (g)+ 1/ 2 O 2 (g) ΔH ∘ B = -90.2 kJ (2 reversed)
4. 2NO(g) → N 2 (g)+ O 2 (g) ΔH ∘ B = -180.4 kJ (eqn 3 x 2)
5. N 2 (g)+2O 2 (g)→2NO 2 (g), ΔH ∘ A =66.4 kJ (eqn 1 x 2)
Express your answer with the appropriate units.
Add equations 4 and 5 to get,
2NO(g)+O 2 (g)→2NO 2 (g) ΔH = -114 kJ
5- Calculate the enthalpy of the reaction
4B(s)+3O 2 (g)→2B 2 O 3 (s)
given the following pertinent information:
1. B 2 O 3 (s)+3H 2 O(g)→3O 2 (g)+B 2 H 6 (g), ΔH ∘ A =+2035 kJ
2. 2B(s)+3H 2 (g)→B 2 H 6 (g), ΔH ∘ B =+36 kJ
3. H 2 (g)+ 1 2 O 2 (g)→H 2 O(l), ΔH ∘ C =−285 kJ
4. H 2 O(l)→H 2 O(g), ΔH ∘ D =+44 kJ
5. 2B 2 O 3 (s)+6H 2 O(g)→6O 2 (g)+2B 2 H 6 (g), ΔH ∘ A = +4070 kJ (eqn 1 x 2)
6. 6O 2 (g)+2B 2 H 6 (g) → 2B 2 O 3 (s)+6H 2 O(g) ΔH ∘ A = -4070 kJ (eqn 5 reversed)
7. 4B(s)+6H 2 (g)→2B 2 H 6 (g), ΔH ∘ B = +72 kJ (eqn 2 x 2)
8. 6H 2 O(l)→6H 2 O(g), ΔH ∘ D = +264 kJ (eqn 4 x 6)
9. 6H 2 O(g)→6H 2 O(l), ΔH ∘ D = -264 kJ (eqn 8 reversed)
10. 6H 2 (g)+ 3O 2 (g)→6H 2 O(l), ΔH ∘ C =−1710 kJ (eqn 3 x 6)
11. 6H 2 O(l)→ 6H 2 (g)+ 3O 2 (g) ΔH ∘ C = +1710 kJ (eqn 10 reversed)
Add equations 6, 7, 9 and 11 to get
4B(s)+3O 2 (g)→2B 2 O 3 (s) ΔH ∘ = -2552 kJ
Express your answer with the appropriate units.
6- Ozone, O ...

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