Achieve week 3 and 4 #6

[Nathalia Garibay 1D]

Hello,

Can someone explain to me how to approach #6 on the achieve? How would we know which quantity is equal to Delta H rxn?

Any help would be appreciated :)

[Ethan Crofut 1E]

Look at each reaction and think about, what happens in the process of converting the reactants to products. Are you breaking bonds? Forming bonds? Which one can you tell is a combustion reaction? Which reaction is a compound being formed from its constituent elements in their natural state?

Remember that breaking bonds requires energy (equal to the bond energy), and forming bonds releases energy (equal to the bond energy).

[ishankhurana2D]

Hello! You can determine which quantity is equal to Delta H rxn by classifying the reaction. In this case, the reactions are either:

Combustion reactions: X + _O₂ (aq) --> _CO₂ (aq) + _H₂O (l), in which case Delta H rxn = Delta H of the combustion of X

Synthesis reactions: X + Y --> XY, in which case Delta H = the bond energy (negative, bonds are formed) of XY

Decomposition reactions: XY --> X + Y, in which case Delta H = the bond energy (positive, bonds are broken) of XY = the energy of an X-Y single bonds (or the # of bonds present)

Synthesis formation reactions: X + Y --> XY, where X and Y are elements in their most stable form (i.e. diatomic molecules for the diatomic elements, C_graphite, etc., in which case Delta H rxn = the Delta H of formation of XY (as XY is being made from "raw" (as stable as possible) molecules or elements.

I hope this helps! Please let me know if you have any other questions, would want more specific help, or if anything is unclear :)

[Danielle Paisley 1H]

Hi! I solved it by carefully looking at all of the reactions and examining what was happening. Ask yourself, "When the reactants and products get converted, what happens?" By doing this, you will determine which one can break the bonds and which one forms the bonds. This will help you to determine the answer. Hope this helps!

[Anna_Aldridge_2C]

Hi!

I remember being a bit confused on how to first approach this question. In order to solve it, I think it is important to observe the reactants and products of the equations, what is being formed/broken, and how it is being formed and broken (basically the types of equations). For example, the first question asks for the reaction of methane and O2, resulting in carbon dioxide and water. As a result of the reactants and products, the equation is an example of combustion and by process of elimination, you can chose the enthalpy of combustion for the first problem. For the other equations, I think it is helpful to observe the similarity and differences between them, and if they are endothermic and exothermic. This should help narrow down options and result in the answers for each. Hope this helps!

[Joyce Lee 1K]

Hello! For this question, I mostly just looked at the reaction and tried to understand what was happening in the equation. This included whether bonds were being broken or formed along with which reactants were converted to products and such. I used this to then evaluate how that would affect the reaction.