Question

calculate the enthalpy change

*see attachment*

Answer 1

Ok, cool. So we're looking for the enthalpy change from solid to a gas.

Answer 2

From the pic, you can easily see that go to from ice to liquid water, there is an enthalpy change of +6 kJ.

Answer 3

However, for the top one, they give you the enthalpy change of a gas to a liquid. So, the enthalpy change from going from liquid form to gas form will be the opposite of the number. c:
To get the total, add the two enthalpies you got up.

Answer 4

i dont understand what enthalpy is lol

Answer 5

Enthalpy is a fancy word for how much heat was exchanged lol.
So, you would expect enthalpy to be positive when going from a solid to a liquid. Or a liquid to a gas.

Answer 6

so in this case it is positve bc we are going from solid to gas

Answer 7

Mhm.c:

Answer 8

so would i have to do -285.9 kJ+6.0 kJ

Answer 9

Nope. Look at the picture, the reaction goes from a gas to a liquid, that's -285.9 kJ.
So, to go from liquid water to the gas, you need 285.9 kJ.
Now, you can add the two enthalpy changes for the total change.

Answer 10

so -285.9 kJ+ 285.9 kJ+6?

Answer 11

Nuuu. We're not using the -285.9 kJ. That was just to get the +285.9 kJ. We just want the enthalpy needed to from from liquid to gas.

Answer 12

ergh ok so 285.9 kJ+6.0 kJ?

Answer 13

Mhm. c:

Answer 14

thank heavens
so it is 291.9 kJ

Answer 15

Mhm.

Answer 16

@iPwnBunnies ok it says +291.9 is wrong........

Answer 17

Ugh, are you srs. .-. Sorry. >.<

Answer 18

I'm not sure how that's wrong. Do you have to include the units too?

Answer 19

ill screenshot what it says

Answer 20

That really makes no sense. .-. If you have another shot, try the other positive one. Sorry about this. DX

Answer 21

its ok at least u tried

Answer 22

@iPwnBunnies i think it wants me to do -285.9kJ+6kJ

Answer 23

Ugh, I really don't know. I don't know why. .-. You're going from a liquid to a gas, not a gas to a liquid.

Answer 24

https://answers.yahoo.com/question/index?qid=20131106144122AA4EkOs even shows my answer right.....

Answer 25

.-.

Answer 26

the most easy way to remember is
enthalpy change of reaction = product - reactant
ur equation is
\[H _{2}O \rightarrow H _{2} + 1\div2 O _{2}\]

the tricky part is this

Answer 27

look at it very carefully
in first equation they are showing that
from H2 GAS and O2 GAS u get water LIQUID

originally in your equation
water SOLID is broken to H2 GAS and O2 GAS

that means u do not need liquid, also that means the equation of 'from H2 GAS and O2 GAS u get water LIQUID' and enthalpy change -285.9 is reverse of what you need, meaning if u switch places it's gonna be
water LIQUID break down to H2 GAS and O2 GAS
and of course enthalpy change will be with opposite sign thus +285.9
what does this new equation show? it shows Enthalpy change of formation of H2 and O2 gas from LIQUID water
now you have value for your product side
lets go to reactant side in original equation, its water SOLID right?
ok, moving on to the next equation
in next equation its turning from from water SOLID to water LIQUID and enthalpy change is +6
again u do NOT need water liquid, thus switch places
now its gonna be turning from water LIQUID to water SOLID and enthalpy change will by with opposite sign thus -6
if u notice here, from liquid to solid water is basically enthalpy change of Formation of solid water right?
so now u have ur reactant side also

finally use the formula
\[\Delta H = product - reactant \]
thus = +285.9 - (-6) = +291.9 kj

hope its clear now :D
@iPwnBunnies @highschoolmom2010

Answer 28

but it still says that my answer was wrong @Somy

Answer 29

@highschoolmom2010 where is that question from?

Answer 30

my chemistry assignment
i did it and i was told to see why i got it wrong and i dont see how

Answer 31

so what's the answer supposed to be? @highschoolmom2010

Answer 32

im not sure i keep getting +291.9 kJ

Answer 33

yeah but what is the right answer @highschoolmom2010

Answer 34

is the answer -279.9 kJ ? coz this one also does make sense

Answer 35

i tried doing -285.9+6 also but was unsure which way to to it

Answer 36

no, the thing is that i even tried Hess cycle and it gave me same answer @highschoolmom2010

Answer 37

so im confused on which one you are sating is correct.