madey21
Answered

Hess' Law: Combustion of Ethanol

Reaction 2 needs to be tripled to connect with the goal equation.

[tex]\[ \text{2: } H_2 + \frac{1}{2} O_2 \rightarrow H_2O, \Delta H = -286 \text{kJ} \][/tex]

What is the adjusted enthalpy for Reaction 2?

A. [tex]\( +858 \text{kJ} \)[/tex]
B. [tex]\( -858 \text{kJ} \)[/tex]
C. [tex]\( +286 \text{kJ} \)[/tex]
D. [tex]\( -286 \text{kJ} \)[/tex]



Answer :

Sure! To solve for the adjusted enthalpy change for Reaction 2 when it needs to be tripled, we can follow Hess' Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps of the reaction.

Given the enthalpy change for the original Reaction 2:
[tex]\[ H_2 + \frac{1}{2} O_2 \rightarrow H_2O , \Delta H = -286 \, \text{kJ} \][/tex]

We need to multiply this reaction by 3, as indicated. Let’s denote the multiplier by 3. Therefore, the reaction becomes:
[tex]\[ 3 \times \left( H_2 + \frac{1}{2} O_2 \rightarrow H_2O \right) , \Delta H_{\text{adjusted}} \][/tex]

When we multiply the reaction coefficients by 3, we also need to multiply the enthalpy change by 3 to maintain consistency:
[tex]\[ \Delta H_{\text{adjusted}} = 3 \times (-286 \, \text{kJ}) \][/tex]

Therefore, the adjusted enthalpy change for the reaction is:
[tex]\[ \Delta H_{\text{adjusted}} = -858 \, \text{kJ} \][/tex]

So, the correct adjusted enthalpy for Reaction 2 when it is tripled would be:
[tex]\[ \boxed{-858 \, \text{kJ}} \][/tex]