Achieve week 3 and 4 (Question 8)

[eopeyany 3D]

Hi, I had a question regarding Question 8 on Achieve week 3 and 4. In regards to the following two questions which ask us to calculate the amount of heat or the CS2 produced, would we still use the exact same methods or different ones in regards to the lecture?
Carbon disulfide can be prepared from coke (an impure form of carbon) and elemental sulfur.
4C(s)+S8(s)⟶4CS2(l) Δ H∘=+358.8 kJ
Calculate the amount of heat absorbed in the reaction of 179 g of carbon with excess sulfur.
Calculate the amount of CS2 produced when 391 kJ of heat is absorbed.

[David Song 3E]

For this question, we need to essentially "scale" the entire reaction by the number of moles that we have. So, for example, for the first part where we have 1.33 moles of S8 that react, we would need to scale the entire reaction by a factor of x1.33 (including the enthalpy change) since the reaction shows we have 1 mole of S8 when in reality we have 1.33. Thus, we would find that our enthalpy change would be 358.8 kJ x 1.33 = 477 kJ.

This would kind of fall into the first method of using Hess's law except that we are not working with multiple reactions but rather just the different factors of one reaction.

[lanatruong]

Hi, yeah I agree with the other response where you would utilize the given deltaH to cancel out the moles you found to ultimately get the amount of heat absorbed.

[lanatruong]

Hi, yeah I agree with the other response where you would utilize the given deltaH to cancel out the moles you found to ultimately get the amount of heat absorbed.

[lanatruong]

Hi, yeah I agree with the other response where you would utilize the given deltaH to cancel out the moles you found to ultimately get the amount of heat absorbed.

[905775469]

I completely agree with the above statements but I think it is important to understand why we do the scaling of the products and reactants to the amount of heat produced. The amount of heat produced is standard enthalpy which is the change in enthalpy from producing one mole of products from its reactants in their standard states.

[505736451]

Following up with the previous replies, you will also need to scale the problem based on the amount of CS2 for the second part of the problem. So it is important to remember that 358.8 KJ produces 4 moles of CS2, so use a ratio to find the amount of moles of CS2 produced from 391 KJ