homechemistry
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HELP!
I fumbled on two questions from my assigned work. Any help is appreciated!
1. If a reaction releases 50kJ of heat, what is the change in enthalpy for the reaction?( indicate whether this change is positive or negative)
2.If the rate of reaction is 3.0 x 10^-3 M/s at 20 degrees Celsius, what would the rate be if the temperature was increased to 40 degrees Celsius?
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Etaoin Shrdlu
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What work have you done on it so far?
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homechemistry
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i think the first one is - 50 kJ and the second i have no clue
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Zombie
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Dude... You are so screwed.
These guys will make you figure it out.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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Molecular Manipulations
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It's considered common courtesy to show an attempt at solving the questions, but since you posted this in Beginnings, and since the answers are so
easy, I'll give you some help.
#1: Energy released is indicated negatively to show that the enthalpy in the atom that bonds (releasing energy) decreases afterwards (because the
energy is given off). So the answer is: the change in enthalpy = -50kJ.
#2: This one's not really possible to answer 100% without knowing the specific chemical reaction who's rate is in question. However I'm going to bet
your teacher or textbook mentioned an approximation regarding the increase in rate and temperature. Usually they say that for every 10°C increase the
rate doubles. This generalization has many exceptions, but is for the most part is correct.
Since the temp increases by 20°C the reaction rate should double, twice.
I'll let you do the math here, since I already gave you the answer.
[EDIT]
I love this quote:
[Edited on 18-4-2015 by Molecular Manipulations]
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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j_sum1
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FWIW, I would consider both of these to be poorly-framed questions. The second for the reasons that MM stated. The rate rule required is a rule of
thumb only and without specifics it is difficult to have any confidence in the answer at all.
The first does not specify a quantity. One assumes that the figure given is per mole, but it is a bit on the high side for many reactions. It may be
per kg of a particular reactant or... well, who knows?
Trying to teach a meaningful concept in the absence of a meaningful context is kinda couterproductive. You can end up knowing all the answers and
still not having a clue. (The same goes for assessment as for teaching.)
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homechemistry
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for the second question i came up with the answer of 1.2 x 10^-2 M/s.
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Etaoin Shrdlu
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Doesn't matter. The question asks for the enthalpy change of the reaction, and gives heat released during the reaction. No need to write it in terms
of moles or mass.
The second question was iffy though.
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j_sum1
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Quote: Originally posted by Etaoin Shrdlu  |
Doesn't matter. The question asks for the enthalpy change of the reaction, and gives heat released during the reaction. No need to write it in terms
of moles or mass.
The second question was iffy though. |
I know that technically it doesn't matter. But it is not that
meaningful either.
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Etaoin Shrdlu
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| Quote: Originally posted by j_sum1 | | Quote: Originally posted by Etaoin Shrdlu |
Doesn't matter. The question asks for the enthalpy change of the reaction, and gives heat released during the reaction. No need to write it in terms
of moles or mass.
The second question was iffy though. |
I know that technically it doesn't matter. But it is not that
meaningful either. |
Sure it is. I'm assuming this is highschool stuff and they're just trying to get across the basic concept that enthalpy change is equal to energy
transferred from the environment before relating it to anything specific. Isn't enthalpy generally introduced in relation to a generic "system" first?
EDIT: vagueness
[Edited on 4-18-2015 by Etaoin Shrdlu]
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homechemistry
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so is my answer to number 2 correct?
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