which type of reaction has the largest release of energy per gram of material?

Question

a. break down of 1g of salt into its molecular components?
b. break down of 1g of sugar into its molecular components?
c. burning 5 large logs of wood
d. burning 3 tons of coals?

I think its B, but I am not sure. Please explain

Answer 1

Salt and sugar are stable molecules, so you need to GIVE energy to break them down to their molecular components.
Burning wood implies decomposing the long molecular chains so that those can be burned and that decomposition requires some energy; while coal is already made of shorter hydrocarbon chains, when it is not of a grade that makes it nearly pure carbon.
So the answer is D.
No wonder coal is used as a fuel, which is considered superior to wood in this respect.

Answer 2

Before you start jumping to conclusions about what the answer is, you need to know what is it you are calculating. In this case you are calculating the enthalpy of reactions. But here's the twist to this question, there are two different types. Salt requires that you know its standard enthalpy of formation, but the others require that you use Hess' Law to determine the enthalpy of combustion. In fact you can rule out the first two because 'breaking down' implies energy needs to be inputted.

So you need only consider wood and coal. So simply apply Hess' Law to wood and coal and then convert from moles to grams. Hint: you can ignore the quantity given because they don't ask about total enthalpy.

I should point out that the calulations are not difficult, but it is essential that you know how to calculate Hess' Law and the, similar, Born-Harber Cycle. These concepts are very popular on exams, not knowing them can cost a lot of marks.

Answer 3

Based on the descriptions and my honest choice [usually biased] I fit AB and O with none of the negatives though my confidence may be perceived for arrogance Sun - Aquarius Moon - Aries Again bias from selection :/.... people choose what they choose and it may not be the truth also only 4 types... Dunno my actual blood type :/... but I wouldn't be surprised if it was AB or O... though that is 50% chance combined If I had to fit each to an element O = Fire or Water B = Fire + Sag + Pisces maybe Water AB = Air or Earth definitely A = Earth... specifically Virgo.... Also Fixed Signs and Water signs, probably fixed Water too These descriptions are a bit too much of each sign and not hard wired into a clear decision But again like the previous question I would say if someone had like a setup with Cancer sun Scorpio moon and lots of water with no Air and then "Got" [Chose] Sanguine... I would be like duuuuuuuuuuuude.............BS!!!!!!!!!!... Liar!! Unlike other people I'm not politically correct, I'm honest... And astrologers don't like working backwards, or saying a sign isn't more of "this, or 'that" ... I have no interest in doing that especially if it's the truth....

Answer 4

3 TONS of coal... a ton is a lot, think about it. 1 ton =907,184.74 grams . since you have three of them that is 2,721,554.22 grams

One very common source of energy is the burning of coal. salt is very stable, sugar is pretty stable so you need to put energy the reaction, and 5 large logs are not in the weight class of 3 Tons of coal.

Coal is actually very efficient for fuel, but nuclear energy is even more efficient.

Answer 5

Since this is per gram, the amounts quoted don't mean squat. Breaking down anything requires energy, you don't get energy from it. So (a) and (b) require an input of energy. Now, lets see, which one gives off more heat per unit weight for burning, coal or wood? For this, just remember that trains carried wood before they carried coal, why did they switch? More heat output per gram for coal than for wood. So answer (d)