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Using the following bond energies:
Bond Bond Energy (kJ/mol)
C ≡ C 839
C-H 413
O=O 495
C=O 799
O-H 467
Estimate the heat of combustion for one mole of acetylene
C2H2(g)+5/2O2(g)→2CO2(g)+H2O(g)
a. 1228 kJ
b. -1228 kJ
c. -447 kJ
d. +447 kJ
e. +365 kJ

Respuesta :

Answer:

The answer is "Option b".

Explanation:

Given equation and value:

[tex]\Rightarrow C_2H_2 \ (g)+ \frac{5}{2}O_2 \ (g) \longrightarrow 2CO_2\ (g)+H_2O\ (g)[/tex]

[tex]\left\begin{array}{ccc}C \equiv C&839\\C-H &413\\O=O &495\\ C=O &799\\ O-H &467 \end{array}\right \\\\[/tex]

calculating equation value:

[tex]\Rightarrow 839 + 2(413) +\frac{5}{2} (495) \longrightarrow 2(2)799+2 \times 467 +E[/tex]

[tex]\Rightarrow 839 + 826 +1237.5 = 3196+934 +E\\\\\Rightarrow 2902.5 =4130 +E\\\\\Rightarrow 2902 = 4130 +E\\\\\Rightarrow 2902 - 4130 +E\\\\\Rightarrow E = -1228 \ KJ \\\\[/tex]

The heat(enthalpy) of combustion of acetylene = -1228 kJ

The heat of combustion refers to the amount of heat released when 1 mole of a substance is burned.

The chemical reaction is given in the equation;

  • [tex]\mathbf{C_2H_{2(g)} + \dfrac{5}{2}O_{2(g)} \to 2CO_{2(g)}+H_2O_{(g)}}[/tex]

The bond energy of the reactant is:

  • [tex]\mathbf{=( 1 \times C \equiv C) + ( \dfrac{5}{2} O =O)+(2 \times (C-H))}[/tex]  

Following the bond energies given in the question, we have:

= ( 1 × 839) +(5/2 × 495) +(2 × 413)

= 2902.5 kJ

The bond energy of the product is:

  • [tex]\mathbf{4 \times C=O ) + (2 \times O-H)}[/tex]

= (4× 799) +(2 × 467)

= (3196 + 934) kJ

= 4130 kJ

The heat(enthalpy) of combustion of acetylene = bond energy of reactant - bond energy of the product.

The heat(enthalpy) of combustion of acetylene = 2902.5 kJ - 4130 kJ

The heat(enthalpy) of combustion of acetylene = -1227.5 kJ

≅  -1228 kJ

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