what amount of heat energy is produced when 1.0 kg of CO2 (g) is produced durint the combustion of octane

7 years ago

Answered By Vincent E

First, you can write out and balance the combustion equation for octane, C_{8}H_{18(l)} + (25/2)O_{2(g)} -> 8CO_{2(g)} + 9H_{2}O_{(g).}

Then you can find the amount of moles of carbon dioxide using the formula n = m/M, since the mass of CO_{2 }is given in the problem.

Then you can use mole ratios to find the moles of the other species.

You can then use the following equation to find (delta)H. Be sure to use the moles you calculated using the mole ratios, and not the stoich ratios. If the reaction were in stoichiometric ratios, you would be producing 352 kg of carbon dioxide!

Keep in mind that you should be getting a negative number, since this is an exothermic reaction.

Next, use the mass and molar mass of CO_{2} produced.

n (moles) = mass / molar mass

n = 1000g/(44.01g/mol) = 22.72 mol CO_{2}

Use this to find the moles of the other compounds in the reaction.

Then you need to calculate the heat of reaction ( $\bigtriangleup H_r$?Hr ). You can do this by looking in your data tables for the heat of formations (kJ/mol) for each of the compounds, and put them into the following equation. In the equation, n is the number of moles required for the reaction to occur (the moles that you calculated previously).

7 years ago

## Answered By Vincent E

First, you can write out and balance the combustion equation for octane, C

_{8}H_{18(l)}+ (25/2)O_{2(g)}-> 8CO_{2(g)}+ 9H_{2}O_{(g).}Then you can find the amount of moles of carbon dioxide using the formula n = m/M, since the mass of CO

_{2 }is given in the problem.Then you can use mole ratios to find the moles of the other species.

You can then use the following equation to find (delta)H. Be sure to use the moles you calculated using the mole ratios, and not the stoich ratios. If the reaction were in stoichiometric ratios, you would be producing 352 kg of carbon dioxide!

Keep in mind that you should be getting a negative number, since this is an exothermic reaction.

## Attached Whiteboard:

Play Drawing7 years ago

## Answered By Deeti P

The first step is to write out the combustion reaction.

octane + oxygen ---> carbon dioxide + water vapour

Write this reaction out with the correct molecular formulas. Then balance it. You will end up with the following:

C

_{8}H_{18(g)}+ (25/2) O_{2(g)}→ 8 CO_{2(g)}+ 9 H_{2}O_{(l)}Next, use the mass and molar mass of CO

_{2}produced.n (moles) = mass / molar mass

n = 1000g/(44.01g/mol) = 22.72 mol CO

_{2}Use this to find the moles of the other compounds in the reaction.

Then you need to calculate the heat of reaction ( $\bigtriangleup H_r$?Hr ). You can do this by looking in your data tables for the heat of formations (kJ/mol) for each of the compounds, and put them into the following equation. In the equation, n is the number of moles required for the reaction to occur (the moles that you calculated previously).

$\bigtriangleup H_r=\sum nH_{f,products}-\sum nH_{f,reactants}$?Hr=∑nHƒ ,products−∑nHƒ ,reactants

This should give you an answer in kJ. Note that since combustion is exothermic, your answer will be negative.

7 years ago

## Answered By Deeti P

Correction: The equation above should read

C8H18(g) + (25/2) O2(g) → 8 CO2(g) + 9 H2O(g)

*Water is a gas