Chemistry: Algebra Combining Equations [Enthelpy]

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To solve the lab analysis question, the discussion emphasizes the application of Hess's Law to combine the given equations and their enthalpy values. The user seeks clarification on whether to change the signs of the enthalpy values before adding them to derive the enthalpy of combustion for magnesium. It is confirmed that the signs should be altered as necessary based on the direction of the reactions. The final step involves plugging in the values after the equations are combined. Understanding these steps is crucial for accurately calculating the enthalpy change.
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Hi, I am stuck on this one question for a lab analysis I am doing. I missed the class where the teacher explained this and a lot more stuff. I also recall a question like this on a test I wrote on friday:smile:

Anyway here it is:

Algebraically combine equations (2), (3), and (4) and their corresponding [Change in Enthalpy] values, to get (1) and [Change in Enthalpy] of combustion of magnesium.

I just need to know how to do it, I can plug in the values after right?

Let me know! thanks in advance!
 
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Have you learned about Hess's Law?
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Your question requires a direct application of Hess's Law.
 
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Ya I have learned Hess' law but I'm still unsure...

So do I change the signs then add them together to get the enthalpy of equation 1?
 
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