PAC 110 BASIC CHEMISTRY
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Course Content
Naming of Simple Compounds and Chemical Thermodynamics (09 May 2023).pptx
CHEMICAL THERMODYNAMICS (15 MAY 2023).pptx
PAC 110 Atomic Structure and Chemical Bonding (3 April 2023).pptx
Chemical Bonding and Atomic Structure (27 March 2023).pptx
Atomic Structure (06 March 2023).pptx
Atomic Structure - 27 February 2023.pptx
PAC 110 BASIC CHEMISTRY INTRO 2023.pptx
PAC 110 course content to be taught by (Prof B.A. Aderibigbe)
PAC 110 course content to be taught by (Prof B.A. Aderibigbe)
Lecture 1: Basic concepts of matter
Lecture 1: Basic concepts of matter
Self-practice exercises (1) on Basic concept of matter.pdf
Basic concepts of matter (2) Discussion
Matter can change from one state to another. Discuss factors that contribute to matter to changing states.
Matter can change from one state to another. Discuss factors that contribute to matter to changing states.
Lecture notes on Chemistry and measurement
Lecture notes on Chemistry and measurement
Chemistry and Measurement 1.pdf
Lecture 3 notes (Chemistry and Measurement wih Prof Aderibigbe).pdf
Acid, Bases and Redox Equilbria
Gases part 2 (Prof B. Aderibigbe)
Thermochemistry lectures
Thermochemistry lectures
PAC 110 MAKE UP TEST (PROF B. ADERIBIGBE) 27TH MAY 2023
Due date: 5/27/23, 9:00 AM
Time limit: 120 minutes
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Test
PAC 110 MAKE UP TEST (PROF B. ADERIBIGBE) 27TH MAY 2023
PAC 110 MAKE UP TEST (PROF B. ADERIBIGBE) 27TH MAY 2023
19 minutes remaining
7 OF 38 QUESTIONS REMAINING
Test Content
Page 32 of 38
Question 32
3
Points
The table below shows some values for standard enthalpy changes of combustion.
Substance
incrementHc Ө / kJ mol−1
C(s)
−394
H2(g)
−286
CH4(g)
−890
Use these values in the table above to calculate the standard enthalpy change of the reaction
C(s) + 2H2(g) ® CH4(g)
-210 kJ
-604 kJ
-76 kJ
-318 kJ
The correct answer is -76 kJ.
To calculate the standard enthalpy change of the reaction, we need to use Hess's Law, which states that the total enthalpy change of a reaction is independent of the path taken to get from the reactants to the products.
First, we need to write the balanced chemical equation for the reaction:
C(s) + 2H2(g) → CH4(g)
Next, we can use the enthalpy changes of combustion for each substance to calculate the enthalpy change for the reaction:
ΔHrxn = ΣΔHc°(products) - ΣΔHc°(reactants)
ΔHrxn = [ΔHc°(CH4)] - [ΔHc°(C) + 2ΔHc°(H2)]
ΔHrxn = [-890 kJ/mol] - [-394 kJ/mol - 2(-286 kJ/mol)]
ΔHrxn = -76 kJ/mol
Therefore, the standard enthalpy change of the reaction C(s) + 2H2(g) → CH4(g) is -76 kJ/mol.
To calculate the standard enthalpy change of the reaction C(s) + 2H2(g) -> CH4(g), we can use the values given in the table for the standard enthalpy changes of combustion.
The equation for the reaction is:
C(s) + 2H2(g) -> CH4(g)
We can break down the equation into the combustion reactions for each substance involved:
C(s) + O2(g) -> CO2(g)
H2(g) + 0.5O2(g) -> H2O(l)
CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)
Now, we need to find the standard enthalpy changes for these combustion reactions, using the values given in the table:
C(s) + O2(g) -> CO2(g): ∆H = -394 kJ/mol
H2(g) + 0.5O2(g) -> H2O(l): ∆H = -286 kJ/mol
CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l): ∆H = -890 kJ/mol
To calculate the standard enthalpy change for the reaction C(s) + 2H2(g) -> CH4(g), we can use Hess's Law, which states that the overall enthalpy change for a reaction can be calculated by summing the enthalpy changes of the individual reactions involved.
Since we need the equation to be:
C(s) + 2H2(g) -> CH4(g), we can reverse the first equation and double the enthalpy change:
CO2(g) -> C(s) + O2(g): ∆H = +394 kJ/mol (reversed)
2H2O(l) -> 2H2(g) + O2(g): ∆H = +572 kJ/mol (reversed and doubled)
Now, we can add up the enthalpy changes of the reactions to get the enthalpy change for the overall reaction:
∆H = ∆H(C(s) + O2(g) -> CO2(g)) + ∆H(2H2O(l) -> 2H2(g) + O2(g)) + ∆H(CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l))
∆H = (-394 kJ/mol) + (+572 kJ/mol) + (-890 kJ/mol)
∆H = -118 kJ/mol
Therefore, the standard enthalpy change of the reaction C(s) + 2H2(g) -> CH4(g) is -118 kJ/mol.
So, none of the options given (-210 kJ, -604 kJ, -76 kJ, -318 kJ) are correct.