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Standard Enthalpy of Formation and Calculation of CS2 (l), Slides of Chemistry

The concept of standard enthalpy of formation and provides a formula to calculate it. It also includes an example calculation for the standard enthalpy of formation of CS2 (l) using the given data for CH4(g), O2(g), CO2(g), and H2O(l).

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2021/2022

Uploaded on 09/12/2022

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5.5: Standard Enthalpy of Formation
Standard enthalpy of formation (ΔH0) is the heat change
that results when one mole of a compound is formed from
its elements at a pressure of 1 atm.
SATP: Standard Atmospheric Temperature and Pressure
T = 25oC (298K) P = 1 atm
f
The standard enthalpy of formation of any element in its most
stable form is zero.
5.5
pf3
pf4
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5.5: Standard Enthalpy of Formation

Standard enthalpy of formation (ΔH

0 ) is the heat change

that results when one mole of a compound is formed from

its elements at a pressure of 1 atm.

SATP: Standard Atmospheric Temperature and Pressure

T = 25

o C ( 298K) P = 1 atm

f

The standard enthalpy of formation of any element in its most

stable form is zero.

Calculate the standard enthalpy of formation of CS 2

( l )

given that:

CH

4

(g) ΔH

0 = -74.4 kJ/mol f

CH

4

(g) + 2O 2(g)

CO

2(g)

+H

2

O( l )

O

2

(g) ΔH

0 = 0 kJ/mol f

CO

2

(g) ΔH

0 = -393.5 kJ/mol

f

ΔH

0

r

n ΔH

0 (products) f

= Σ^ n ΔH

0 (reactants) f

ΔH

0

r

[1 ΔH

0 (CO 2

f

+ 1 ΔH

0 (H 2

O)]-[ 1 ΔH

0 (CH 4

)+ 2 ΔH

0 (O 2

)]

f

f

ΔH

0

r

[ 1 (-393.5kJ/mol )+ 1 (-285.8kJ/mol)]

-[ 1 (-74.4kJ/mol) + 2 (0kJ/mol)]

H

2

O(g) ΔH

0 = -285.8 kJ/mol

f

f

ΔH

0

r

-890.7kJ

∆H

0

f

(C

2

H

2(g)

) = +227 kJ/mol

∆H

0

f

(CO

2(g)

) = - 394 kJ/mol

∆H

0

f

(H

2

O

(g)

) = - 242 kJ/mol

ANS: -1257 kJ/mol

Use the values of the heat of formation

given to determine the molar heat

Of combustion for acetylene (ethyne).