chemical reaction

[logistic_guy]

here is the question

One of the best-selling light, or low-calorie, beers is $\displaystyle 4.2\%$ alcohol by volume and a $\displaystyle 12$-oz serving contains $\displaystyle 110$ Calories; remember: $\displaystyle 1$ Calorie $\displaystyle = 1000$ cal $\displaystyle = 1$ kcal. To estimate the percentage of Calories that comes from the alcohol, consider the following questions. (a) Write a balanced chemical equation for the reaction of ethanol, $\displaystyle C_2H_5OH$, with oxygen to make carbon dioxide and water. (b) Use enthalpies of formation in Appendix $\displaystyle C$ to determine $\displaystyle ΔH$ for this reaction. (c) If $\displaystyle 4.2\%$ of the total volume is ethanol and the density of ethanol is $\displaystyle 0.789$ g/mL, what mass of ethanol does a $\displaystyle 12$-oz serving of light beer contain? (d) How many Calories are released by the metabolism of ethanol, the reaction from part (a)? (e) What percentage of the $\displaystyle 110$ Calories comes from the ethanol?


my attemb

i understand when we burn the ethanol the carbon atom turn into carbon dioxide $\displaystyle CO_2$ and the hydrogen atom turn into water $\displaystyle H_2O$ so i need $\displaystyle 2$ carbon dioxide and $\displaystyle 3$ water.

$\displaystyle C_2H_5OH + \cdots \to 2CO_2 + 3H_2O$

this will balance the right side of the equation. still the left side missing $\displaystyle 6$ oxygen atoms since i've $\displaystyle 7$ so i need $\displaystyle 3$ molecular oxygen. this will give me $\displaystyle 6$ atoms. the balance chemical equation

$\displaystyle C_2H_5OH + 3O_2 \to 2CO_2 + 3H_2O$

reaction is my game, but i'm stuck to solve the rest. appendix $\displaystyle C$ say

$\displaystyle ΔH = \sum nΔH_f(products) - \sum mΔH_f(reactants)$

i know this question is basic, but i'm confusedwhat's the idea of this summation?

 

[khansaheb]

$\displaystyle C_2H_5OH + 3O_2 \to 2CO_2 + 3H_2O$

reaction is my game, but i'm stuck to solve the rest. appendix $\displaystyle C$ say

$\displaystyle ΔH = \sum nΔH_f(products) - \sum mΔH_f(reactants)$ ...................................................................(2)

i know this question is basic, but i'm confusedwhat's the idea of this summation?

I believe, in the equation (2) above - H refers to ENTHALPY. Read your textbook to get the correct CONTEXT........

 

[logistic_guy]

I believe, in the equation (2) above - H refers to ENTHALPY. Read your textbook to get the correct CONTEXT........

Your belief is correct. I have a table of enthalpies if you are interested!

 

[logistic_guy]

$\displaystyle \bold{(b)}$

Your belief is correct. I have a table of enthalpies if you are interested!

@khansaheb


$\displaystyle \Delta H = [2\Delta H^{\circ}_f(\text{CO}_2) + 3\Delta H^{\circ}_f(\text{H}_2\text{O})] - [\Delta H^{\circ}_f(\text{C}_2\text{H}_5\text{OH}) + 3\Delta H^{\circ}_f(\text{O}_2)]$

According to the table, we have:

$\displaystyle \Delta H = [2(-393.5) + 3(-285.8))] - [(-277.7) + 3(0)] = -1366.7 \ \text{kJ}$

 

[khansaheb]

Now the rest of this problem awaits......