# Chemistry II

C4H4 (g) + 2 H2 (g) --> C4H8 (g)
Combustion reactions involve reacting a substance with oxygen. When compounds containing carbon and hydrogen are combusted, carbon dioxide and water are the products. Using the enthalpies of combustion for C4H4 (-2341 kJ/mol), C4H8 (-2755 kJ/'mol), and H2 (-286 kJ/mol), calculate the change in heat for this reaction.

We will be happy to critique your work on this. See Hess' Law in your text.

C4H4 (g) --> 4C + 2H2 -2341 kJ/mol
2 H2 (g) --> H2 + H2 2(-286 kJ/mol)
4C + 4H2 --> C4H8 2755 kJ/mol

C4H4 + 2H2 --> C4H8 -158 kJ/mol

No. You have been given the enthalpies of combustion. Write and balance those equations first.

C4H4 + O2 >>> H20 (g) + CO2 balance this
H2+ O2 >>> H2O (g)
C4H8 + O2 >>> H2O (g) + CO2
balance all these. YOu know the heat of combustion in kj/mole of reactant.

From that, you solve for the Heats of formation for C4H4, H2O, and C4H8

Thence, you can calculate the heat of reaction for the reaction. It is an exercise in logic and algebra. Remember, that the heat of combusion is equal to the sum of the heats of formation of the products minus the sum of the heats of formation of the reactants.

1. 👍 2
2. 👎 0
3. 👁 4,229
1. The enthalpies of combustion are determined by these equations:
C4H4(g) + 5 O2(g) ---> 4 CO2(g) + 2 H2O(g) : ÄH = -2341 kJ/mol
2 H2(g) + O2(g) ---> 2 H2O(g) : ÄH = -286 kJ/mol
C4H8(g) + 6 O2(g) ---> 4 CO2(g) + 4 H2O(g) : ÄH = -2755 kJ/mol
If we reverse the last equation, we get:
4 CO2(g) + 4 H2O(g) ---> C4H8(g) + 6 O2(g) : ÄH = 2755 kJ/mol - notice the change in sign

Adding the first 2 equation together, we get:
C4H4(g) + 5 O2(g) + 2 H2(g) + O2(g) ---> 4 CO2(g) + 2 H2O(g) + 2 H2O(g) : ÄH = -2341 kJ/mol + -286 kJ/mol
Combining like items, we get:
C4H4(g) + 2 H2(g) + 6 O2(g) ---> 4 CO2(g) + 4 H2O(g) : ÄH = -2627 kJ/mol

Adding the fourth equation to the last one, we get:
C4H4(g) + 2 H2(g) + 6 O2(g) + 4 CO2(g) + 4 H2O(g) ---> 4 CO2(g) + 4 H2O(g) + C4H8(g) + 6 O2(g) : ÄH = -2627 kJ/mol + 2755 kJ/mol
Removing like items from both sides and summing the energy, we get:
C4H4(g) + 2 H2(g) ---> C4H8(g): ÄH = 128 kJ/mol

1. 👍 0
2. 👎 4
2. This question looks answered it looks as if the final answer is 128kJ/mol is it?

1. 👍 1
2. 👎 0
3. Forgot to account for an additional -286 kj when calculating the heat of combustion for H2 (you have two moles of H2 in the combustion equation, not just one). The final answer should be -158 kJ/mol.

1. 👍 7
2. 👎 0
4. ijede

1. 👍 1
2. 👎 0

## Similar Questions

1. ### Chem

True or false: Wood and other fuels that undergo combustion reactions don’t spontaneously catch on fire just because they are surrounded by oxygen. ood and other fuels that undergo combustion reactions don’t spontaneously

asked by Anonymous on June 23, 2020
2. ### chemistry

Examine the unbalanced equation. CH4 + O2 → CO2 + H2O What is the best classification for the unbalanced equation's reaction, and why? It is a combustion reaction because carbon dioxide (CO2) is emitted as a product. It is a

3. ### science

Examine the following equations. A. 23490Th→23491Pa+0−1e+γ B. 60∗27Co→6027Co+γ C. 23490Th→23088Ra+42He D. 146C→147N+0−1e Which equation or equations represent gamma decay? B C A and B A A and D D C and D Which

asked by Dianni on November 29, 2018
4. ### Chemistry

9. Complete combustion of a 0.20 mole sample of a hydrocarbon, CxHy, yields 0.80 mol of CO2 and 1.0 mol of H2O. What is the empirical formula for the hydrocarbon? A. C2H5 B. C4H5 C. C4H8 D. C4H10 E. C3H8 I have C4H8 Correct?

asked by Trevor on September 29, 2008
5. ### Chemistry

Which of the following is a correct statement about collision theory? A. All collisions lead to chemical reactions. B. Most collisions lead to chemical reactions. C. Very few reactions involve particle collisions. D. Effective

asked by Tina on May 20, 2018
1. ### chemistry

The complete combustion of salicylic acid releases 21.90 kJ of energy per gram of salicylic acid. In a particular bomb calorimeter (initially at room temperature), the combustion of 0.1182 g of salicylic acid, in the presence of

asked by korko on September 25, 2014
2. ### Intergrated Science A

Which answer choices best indicate that a substance has experienced a chemical change? Select all that apply. when the substance changes temperature when the substance changes shape when the substance changes volume when a new

asked by Aubrea colbert on December 12, 2019
3. ### Chemistry

Calculate the ΔHrxn for the following reactions using the heats of formation given in the table at the end of this assignment: a)The complete combustion of methane, CH4, producing water as a liquid. b)The complete combustion of

asked by Beth on February 4, 2015
4. ### Chemistry

The combustion of methanol (CH3OH) forms carbon dioxide and water vapor. A combustion reaction refers to a reaction of a substance with oxygen gas. What is the balanced equation?

asked by Anonymous on October 10, 2017
5. ### Chemistry

Calculate the ΔHrxn for the following reactions using the heats of formation given in the table at the end of this assignment: a)The complete combustion of methane, CH4, producing water as a liquid. b)The complete combustion of

asked by Abby K. on February 2, 2015