enthalpy changes

Watch this thread
This discussion is closed.
wath
Badges: 0
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#1
Report Thread starter 18 years ago
#1
help! i can do enthalpy change reaction questions but i do the arrows and box method and never know which way the arrows should go for combustion or formation reactions. can ne body help me please!
0
George-W-Duck
Badges: 2
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#2
Report 18 years ago
#2
(Original post by wath)
help! i can do enthalpy change reaction questions but i do the arrows and box method and never know which way the arrows should go for combustion or formation reactions. can ne body help me please!
Give an example question and ill do my best to help.
0
Matt the cat
Badges: 0
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#3
Report 18 years ago
#3
(Original post by wath)
help! i can do enthalpy change reaction questions but i do the arrows and box method and never know which way the arrows should go for combustion or formation reactions. can ne body help me please!
By the box method do you mean hess law? with Hess' triangle?....
If its combustion then the arrow will go from the products/reactacnts to the products of combustion (elements)

If it is formation then the arrow will be in the opposite direction.

When you do the end calculation the enthpy change = enthlpy change of reactants - enthpy change of products
0
wath
Badges: 0
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#4
Report Thread starter 18 years ago
#4
thanku!
0
Ralfskini
Badges: 10
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#5
Report 18 years ago
#5
(Original post by oanjum)
for combustion, the arrow goes from the product to the elements.
for formation..from elements to product.

eg..

ch4------> c02+2h20 = combustion
c+2h2---->ch4 = formation.




CO2 and H2O aren't elements.
0
wath
Badges: 0
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#6
Report Thread starter 18 years ago
#6
i think thats just an example of a combustion reaction etc
0
Matt the cat
Badges: 0
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#7
Report 18 years ago
#7
(Original post by wath)
i think thats just an example of a combustion reaction etc
yes?
0
meepmeep
Badges: 0
Rep:
? You'll earn badges for being active around the site. Rep gems come when your posts are rated by other community members.
#8
Report 18 years ago
#8
A nice trick I always use is get your arrows the correct way then follow the other root. If you go forwards down one of the arrows, add the enthalpy change on. If you go the wrong way through an arrow, take the enthalpy change off (be careful of enthalpy changes which are negative, like most combustion reactions and some formation reactions)
0
X
new posts
Back
to top
Latest

How did The Student Room help you with your university application?

Talking to current university students (3)
17.65%
Talking to peers going through the same thing (4)
23.53%
Speaking to student ambassadors from the universities (1)
5.88%
Speaking to staff members from universities (0)
0%
Using the personal statement builder, library or helper service (3)
17.65%
Reading articles about what steps to take (5)
29.41%
Learning about/speaking to Student Finance England (0)
0%
Something else (tell us in the thread) (1)
5.88%

Watched Threads

View All