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Physical Chemistry

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3 Mar 2008 11:16:59 IST

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319

Hess law

None

how to solve numericals based on hess law??

please explain it by giving example n explain each step of ur solution

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Comments (3)

ERAGON007

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Joined: 1 Mar 2008

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3 Mar 2008 11:30:19 IST

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if u use hess law we can add the respective enthalpies of the reactions to get what we want.

try looking at this site:
http://dbhs.wvusd.k12.ca.us/webdocs/Thermochem/HessLawIntro1.html

hope this helps

dev_22oct

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Joined: 27 Feb 2008

Posts: 426

3 Mar 2008 13:37:35 IST

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Q) C(S) + O₂--------------> CO₂(g)

H=?

CALCULATE THE

H FOR THIS REACTION ?

now the data given is

C(S) + 1/2O₂(g) ------> CO(g)

H= -26K CAL

CO(g) + 1/2 O₂ ------> CO₂(g)

H= -68K CAL

now according to the hess law u can get enthalpy change for the reaction by adding these 2 reactions.

there for

H=- 94.0 k cal

Bipin Dubey

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Joined: 23 Jan 2007

Posts: 7942

3 Mar 2008 15:36:24 IST

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When reactions take place, energy in the form of heat is either absorbed (endothermic) or released (exothermic). The amount of heat involved in a reaction depends upon the particular reaction studied or the amount of reactant that is used. Sometimes it is difficult to measure the heat of a reaction directly. Hess?s Law tells us that the amount of heat involved in a reaction is the same, whether the reaction takes place in one or several steps. A modification of this law permits us to find the heat of one step of a reaction if the overall heat and the heats for the other steps are known

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