Question

Using the following equation for the combustion of octane, calculate the heat of reaction for 100.0 g of octane. The molar mass of octane is 114.33 g/mole.

2 C8H18 + 25 O2 -> 16 CO2 + 18 H2O ,deltaH°rxn = -11018 kJ

I got- 4820kJ but the answer is 4820kJ.

why is the answer positive when the delta h is negative?

Answer #1

The heat of reaction in terms of heat of formation values === Heat of formation of products - heat of formation of reactants.

whereas,

Heat of reaction in terms of combustion === Heat of combustion of reactants - heat of combustion of products

This reverse notation is due to the fact that in heat of
formation the desired species is in product side ( eg: for
CO_{2} the equation is C + O_{2} --->
CO_{2} ) whereas for heat of combustion the desired value
is on reactant side (eg: here the desired value is methane since we
are calling it as heat of combustion of methane CH_{4} +
O_{2} ----> CO_{2} + water.)

That is why while calculating through combustion values we use
**-** (deltaH products - deltaH reactants)

Thank you, So, the answer is +4820 kJ

Question 4
Part A
Using the following equation for the combustion of octane,
calculate the heat of reaction for 100.0 g of octane. The molar
mass of octane is 114.33 g/mole.
2 C8H18 + 25 O2 → 16
CO2 + 18 H2O ΔH°rxn = -11018
kJ
Using the following equation for the combustion of octane,
calculate the heat of reaction for 100.0 g of octane. The molar
mass of octane is 114.33 g/mole.
2 C8H18 + 25 O2 → 16...

11. Using the following equation for the combustion of octane,
calculate the amount of grams of carbon dioxide formed from 100.0 g
of octane. C8H18 + O2 → CO2 + H2O ΔH°rxn = -11018 kJ

Calculate heat of combustion reaction of 1.0 g of octane:
2 C8H18 + 25 O2 --> 16 CO2 + 18 H2O
The calorimeter contains 1200 g water, and the temperature
changes from 25.00 deg C to 33.20 deg C. Heat capacity of bomb is
837 J/deg C.

Calculate the deltaH rxn for the production of CO2 and H20 via
propane combustion, using thermochemical equations below. Show all
work! 3 C (s) + 4 H2 (g) = C3H8 (g) Delta H = (-) 103.9 kJ/mol C
(s) + O2 (g) = CO2 (g) Delta H = (-) 393.5 kJ/mol H2 (g) + 1/2 O2
(g) = H2O (g) Delta H = (-)241. 8 kJ/mol Delta H rxn : ?

Octane (C8H18) undergoes combustion according to the following
thermochemical equation:
2C8H18(l) + 25O2(g) 16CO2(g) +
18H2O(l) ∆H°rxn = −10,800
kJ/mol
Given that ∆H°f[CO2(g)] = −394 kJ/mol and ∆H°f[H2O(l)] = −286
kJ/mol, calculate the standard enthalpy of formation of
octane.
a. −326 kJ/mol
b.326 kJ/mol
c.210 kJ/mol
d.-218 kJ/mol

Balance the chemical equation a×C8H18 + b×O2 》c×CO2 +
d×H2O for the combustion reaction of octane by determining the
numbers a,b,c, and d

How many kilograms of CO2 would be produced through
combustion of a gallon (2.6 kg) of octane
(C8H18)?
2 C8H18 (g) + 25 O2 (g) -->
16 CO2 (g) + 18 H2O (g)

Calculate the enthalpy of combustion. Write a balanced
combustion reaction for the oxidation of your substance to CO2 and
H2O. From the stoichiometry of this reaction and the amount of
sample you used, find delta(PV) and thus calculate deltaH. Compare
your value of deltaH with the literature value. deltaH = deltaU +
delta(nRT) = delta U + RT(delta n). the combustion equation is
C12H22O11(s)+12O2(g)arrow12CO2(g)+11H2O(l)
for sucrose. There are 0.1544g of sucrose combusted in a constant
volume calorimeter. Please explain and...

9. Use the following experimentally derived combustion
data to calculate the standard molar enthalpy of formation
(ΔH°f ) of liquid methanol (CH3OH) from its
elements.
2 CH3OH(l) + 3 O2(g) → 2
CO2(g) + 4 H2O(l)
ΔH°rxn = −1452.8 kJ
C(graphite) + O2(g) →
CO2(g)
ΔH°rxn = −393.5 kJ
2 H2(g) + O2(g) → 2
H2O(l)
ΔH°rxn = −571.6 kJ
(1) −238.7 kJ/mol (2) 487.7
kJ/mol (3) −548.3 kJ/mol
(4) 20.1 kJ/mol
(5) 47.1 kJ/mol

Using Hess’ Law, compare the heat of combustion of one liter of
ethanol with the heat of combustion of one liter of octane. The
density of ethanol is 0.789 g/mL and that of octane is 0.703
g/mL.
how do you calculate the number -343.909 kj for CO2 or -241.101
of H2O.. or 200.447kj/mol for C2H4OH?
thank you!

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