Emma Nie
Badges: 4
Rep:
?
#1
Report Thread starter 3 years ago
#1
Given the following data
C(s) + 2H2(g) → CH4(g) ∆H = −75 kJ mol−1
**H2(g) → 2H(g) ∆H = +436 kJ mol−1
which one of the following is the enthalpy change, in kJ mol−1, of the reaction below?
CH4(g) → C(s) + 4H(g)
A−947
B+511
C+797
D+947

Correct answer D
Please explain why. Thank you guys!!!!!
0
reply
h3rmit
Badges: 15
Rep:
?
#2
Report 3 years ago
#2
If you reverse and add the equations until you get the desired equation and do the same to the enthalpies, you'll get the answer.

So, reverse the methane formation equation, to give CH4 -> 2H2 + C with ∆H=75

Double the hydrogen equation to get 2H2 -> 4H with ∆H=872

Add both to give CH4 + 2H2 -> 4H + C + 2H2

The 2H2's are on both sides of the equation, so cancel them to give CH4 -> 4H + C

Then do the same to the enthalpies as you did to the equations (doubling one, and adding both) to give 872 + 75
0
reply
Emma Nie
Badges: 4
Rep:
?
#3
Report Thread starter 3 years ago
#3
(Original post by h3rmit)
if you reverse and add the equations until you get the desired equation and do the same to the enthalpies, you'll get the answer.

So, reverse the methane formation equation, to give ch4 -> 2h2 + c with ∆h=75

double the hydrogen equation to get 2h2 -> 4h with ∆h=872

add both to give ch4 + 2h2 -> 4h + c + 2h2

the 2h2's are on both sides of the equation, so cancel them to give ch4 -> 4h + c

then do the same to the enthalpies as you did to the equations (doubling one, and adding both) to give 872 + 75
life saver!!!!thank you!!!
1
reply
Emma Nie
Badges: 4
Rep:
?
#4
Report Thread starter 3 years ago
#4
Another Question.... Anyone for help.

Substance
ethanamidecarbon dioxidewater
Enthalpy of formation ([img]file:///C:/Users/HUIHUI~1/AppData/Local/Temp/ksohtml/wps478D.tmp.jpg[/img]) / kJ mol−1
−320−394−286

Using the data above, which one of the following is a correct value for the enthalpy of combustion of ethanamide?

A −1823 kJ mol−1
B −1183 kJ mol−1
C −1000 kJ mol−1
D −360 kJ mo1−1


Correct answer B
Please explain why. Thank you guys!!!!!
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

What factors affect your mental health the most right now? (select all that apply)

Lack of purpose or routine (277)
15.42%
Uncertainty around my education (281)
15.65%
Uncertainty around my future career prospects (178)
9.91%
Isolating with family (127)
7.07%
Lack of support system (eg. Teachers, counsellors) (80)
4.45%
Lack of exercise/ability to be outside (150)
8.35%
Loneliness (177)
9.86%
Financial worries (74)
4.12%
Concern about myself or my loved ones getting ill (165)
9.19%
Exposure to negative news/social media (128)
7.13%
Lack of real life entertainment (eg. cinema, gigs, restaurants) (159)
8.85%

Watched Threads

View All