[cartmanike]

Hi guys,
I have a question for school and I am a little confused.

Identify the following reactions as being either endergonic or exergonic.

NAD+ accepts two electrons and a proton to become NADH.

Sucrose undergoes hydrolysis to form glucose and fructose.

During cellular respiration, glucose and oxygen take part in reactions that yield carbon dioxide and water, and release energy.

Using the energy harvest from sunlight, water and carbon dioxide are converted to glucose and oxygen, during photosynthesis.

Since an exergonic reaction will make energy, and an endergonic reaction will require energy to happen, I think that th third bullet is exergonic, and the fourth is endergonic.

But what about the other two? I'm thinking that the sucrose one would need energy to happen, making it endergonic...and the NADH one is exergonic because it makes something new? I don't really know...Thank you

[Luimes13]

hey, i'm doing the same course and i had trouble with that too. i found a link that clearly explained c) and d). maybe it will help you with the others aswell.

my answers were a) endergonic, b) exergonic, c) exergonic, d) endergonic

heres the link
http://www.slideshare.net/ClassOf1/class-of1-photosynthesis-cellular-respiration-17

[rabolisk]

Luimes13's answers are correct, but I don't really understand why these questions are asked as part of grade 12 chemistry. Exergonic means (free) energy releasing and endergonic means energy absorbing from the perspective of the system. It's quite simple to see that reactions 3 and 4 should be exergonic and endergonic, respectively. But the other two reactions, while easily identifiable for someone who has studied biochemistry, has no obvious clues as to whether its  :delta: G should be negative or positive. Basically, the question asks you to judge something that you cannot without more background knowledge about biochemistry. It is an appropriate question to ask in a biochemistry class, but not in grade 12 chemistry, in my opinion.

[sjb]

Luimes13's answers are correct, but I don't really understand why these questions are asked as part of grade 12 chemistry. Exergonic means (free) energy releasing and endergonic means energy absorbing from the perspective of the system. It's quite simple to see that reactions 3 and 4 should be exergonic and endergonic, respectively. But the other two reactions, while easily identifiable for someone who has studied biochemistry, has no obvious clues as to whether its  :delta: G should be negative or positive. Basically, the question asks you to judge something that you cannot without more background knowledge about biochemistry. It is an appropriate question to ask in a biochemistry class, but not in grade 12 chemistry, in my opinion.

Hmm, interesting point. Certainly during *my* grade 12 (I think, can we confirm the age, location and education level, here), we were doing delta-G calculations with molecules etc, so question 2 would not be outside the realms of impossibility. Question 1, perhaps, might be a little harder.

[rabolisk]

Luimes13's answers are correct, but I don't really understand why these questions are asked as part of grade 12 chemistry. Exergonic means (free) energy releasing and endergonic means energy absorbing from the perspective of the system. It's quite simple to see that reactions 3 and 4 should be exergonic and endergonic, respectively. But the other two reactions, while easily identifiable for someone who has studied biochemistry, has no obvious clues as to whether its  :delta: G should be negative or positive. Basically, the question asks you to judge something that you cannot without more background knowledge about biochemistry. It is an appropriate question to ask in a biochemistry class, but not in grade 12 chemistry, in my opinion.

Hmm, interesting point. Certainly during *my* grade 12 (I think, can we confirm the age, location and education level, here), we were doing delta-G calculations with molecules etc, so question 2 would not be outside the realms of impossibility. Question 1, perhaps, might be a little harder.

To be clear, nothing would be impossible if you were given the data. After all, you could be given data for  :delta: G of formation of NADH, NAD⁺, and H⁺ (if such data exists). I was assuming that the question was asking the students to judge based on (at their level) vague chemical intuition, rather than giving them values from a table and asking to calculate, and then state whether or not the reactions are endergonic or exergonic. I am also assuming that grade 12 is equivalent to US grade 12, the last year of secondary school before college.

[Luimes13]

Rabolisk,

I am taking the same course and this is a biology question for a biology course.

[rabolisk]

Oh, this is for a biology class. Then I suppose you should know that hydrolysis of polymers to monomers (reaction 2) is exergonic. 1 is a bit tougher, but if you realize that the opposite process (oxidation of NADH) is used for oxidative phosphorylation to produce ATP, then you can see that it should be endergonic (although this isn't exactly true in it of itself). I still think this is a bit detailed and involves too much chemistry for a grade 12 biology class, but that's just based on my experience.