Hi joy,

Thanks for your question. I can understand the confusion, and the issue is a matter of perspective: whether you calculate the 'final minus initial' energy VS. 'initial minus final' energy. You are right that $\Delta H$ is negative for exothermic reactions, and $\Delta H$ is calculated as 'final total energy minus initial total energy'.

However, 'Q' is the energy released by the system. If the system releases energy to the environment, we say that 'Q' is positive. We find 'Q' by calculating 'initial minus final' energy of the system, and since the initial mass-energy is greater this difference is positive.

Hope this helps,
Mr. Dychko

Hi Joy,

I'm really glad the videos are helpful. As for the odd numbers, I do have the intention of doing the rest, but at the moment I'm on paternity leave, so it won't be for the next few months. I'm afraid they might not be done in time for your course if it's a semester class. It's good that you've mentioned wanting these odds since I wasn't sure if many courses cover the chapters for which odds are missing (only 7 chapters). Which of these chapters is your course covering: 22, 25, 28, 29, 32, or 33?

Thank you so much Sir, I understand now. I am so gratefful to the Giancoli answers team who have made possible the posting of these videos online. Explanations are very clear. I need all the Odd numbered solutions too for the rests of the Chapters that were posted with Even Numbered Solutions only. Are they available now?

Thank you so much. God bless you all at Giancoli Answers.

Joy

I am confused: he said, the reaction is exothermic. But why is the energy positive? Because in exothermic reactions delta H is negative.