CHE 131 Lecture Notes - Lecture 19: Stoichiometry, Aqueous Solution, Thermochemistry
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Chemical energy is released or absorbed from reactions in various forms. The most easily measurable form of energy comes in the form of heat, or enthalpy. The enthalpy of a reaction can be calculated from the heats of formation of the substances involved in the reaction:
?H?rxn=? np?H?f(products)?? nr?H?f(reactants)
where n represents the stoichiometric coefficients.
Calculate the standard enthalpy change for the reaction
2A+B?2C+2D
Use the following data:
Substance | ?H?f (kJ/mol) |
A | -247 |
B | -413 |
C | 213 |
D | -475 |
?H?rxn =
Part A
What is
?
H
?
rxn
for the following chemical reaction?
C
S
2
(g)+2
H
2
O(l)?C
O
2
(g)+2
H
2
S(g)
You can use the following table of standard heats offormation
(?
H
?
f
)
to calculate the enthalpy of the given reaction.
Element/ Compound | Standard Heat of Formation (kJ/mol) | Element/ Compound | Standard Heat of Formation (kJ/mol) |
H(g) | 218 | N(g) | 473 |
H 2 (g) | 0 | O 2 (g) | 0 |
H 2 O(l) | ?285.8 | O(g) | 249 |
C S 2 (g) | 116.7 | H 2 S(g) | ?20.60kJ |
C(g) | 71 | C O 2 (g) | ?393.5kJ |
C(s) | 0 | HN O 3 (aq) | ?206.6 |
Express the standard enthalpy of reaction to threesignificant figures and include the appropriate units.
Part A
What is
?
H
?
rxn
for the following chemical reaction?
C
S
2
(g)+2
H
2
O(l)?C
O
2
(g)+2
H
2
S(g)
You can use the following table of standard heats offormation
(?
H
?
f
)
to calculate the enthalpy of the given reaction.
Element/ Compound | Standard Heat of Formation (kJ/mol) | Element/ Compound | Standard Heat of Formation (kJ/mol) |
H(g) | 218 | N(g) | 473 |
H 2 (g) | 0 | O 2 (g) | 0 |
H 2 O(l) | ?285.8 | O(g) | 249 |
C S 2 (g) | 116.7 | H 2 S(g) | ?20.60kJ |
C(g) | 71 | C O 2 (g) | ?393.5kJ |
C(s) | 0 | HN O 3 (aq) | ?206.6 |
Express the standard enthalpy of reaction to threesignificant figures and include the appropriate units.