Achieve HW #5

[Kaleigh Olla 1L]

Question #5 on the week 3-4 achieve says:

Consider these reactions, where M represents a generic metal.

2M(s)+6HCl(aq)⟶2MCl3(aq)+3H2(g) H1=−678.0 kJ

HCl(g)⟶HCl(aq) ΔH2=−74.8 kJ

H2(g)+Cl2(g)⟶2HCl(g) ΔH3=−1845.0 kJ

MCl3(s)⟶MCl3(aq) ΔH4=−258.0 kJ

Use the given information to determine the enthalpy of the reaction

2M(s)+3Cl2(g)⟶2MCl3(s)

I honestly have no idea where to start on this one. I know I need to manipulate the enthalpies and reactions somehow, but can anyone help me understand how?

[Vicky Tong 3E]

Hi! This one can be a little tricky if you don't pay attention to the state of the molecules. First, you need to know that all the reactions will be manipulated since you are trying to achieve 2M(s)+3Cl2(g)⟶2MCl3(s). For the first reaction, you can leave it alone since you want 2M(s). For the second reaction, you will need to multiply it by 6 in order to get rid of the HCl(aq). For the third reaction, you will need to multiply it by 3 in order to get rid of H(g) and HCl(g). For the final reaction, you will need to inverse and multiply it by 2 to get rid of the MCl3(aq).

While you're following these steps, write everything out to ensure that you understand that process as to how you reached the final reaction. Remember that in order to find the total enthalpy, you need to multiply the individual enthalpies that you also multiplied by in the reaction, and whatever you inversed, the sign of the enthalpy will be the opposite. Hope this helps!

[hanniaghernandez]

Hi! This one can be a little tricky if you don't pay attention to the state of the molecules. First, you need to know that all the reactions will be manipulated since you are trying to achieve 2M(s)+3Cl2(g)⟶2MCl3(s). For the first reaction, you can leave it alone since you want 2M(s). For the second reaction, you will need to multiply it by 6 in order to get rid of the HCl(aq). For the third reaction, you will need to multiply it by 3 in order to get rid of H(g) and HCl(g). For the final reaction, you will need to inverse and multiply it by 2 to get rid of the MCl3(aq).

While you're following these steps, write everything out to ensure that you understand that process as to how you reached the final reaction. Remember that in order to find the total enthalpy, you need to multiply the individual enthalpies that you also multiplied by in the reaction, and whatever you inversed, the sign of the enthalpy will be the opposite. Hope this helps!

Thank you so much for this! I know I was not the person who asked for help on this bus as I was looking for help this helped realize that the state eg. (aq)(s)(l) is crucial in solving this problem and it was what I was missing!

[Jacqueline Vargas 3L]

The previous responses were really helpful for me as well!

Just a note for anyone else working through this problem, make sure to be careful with the signs as you multiply and add the enthalpies! Especially when you input your answer into achieve. I had the right process but forgot about the signs, so I kept inputting the wrong value.