Kaplan Q:Chemistry K of reverse rxn

[hokie4life]

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The equilibrium constant for Reaction 1 is K. What is the equilibrium constant for Reaction 2?
Reaction 1: A + 2B...> 2C + D
Reaction 2: 2C + D -->A + 2B
B. –K
C. 1/K

why is it C and not B? It's the same rxn but backwards so shouldn't the answer be -K?​

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[dantheman2007]

the rules are:
when you reverse a rxn you take the reciprocal
when you halve a rxn you take the square root.
best,
dan

 

[shane.]

The equilibrium constant for Reaction 1 is K. What is the equilibrium constant for Reaction 2?
Reaction 1: A + 2B...> 2C + D
Reaction 2: 2C + D -->A + 2B
B. –K
C. 1/K

why is it C and not B? It's the same rxn but backwards so shouldn't the answer be -K?​

​

​

K1 = [D][C]^2 / [A]^2

K2 = [A]^2 / [D][C]^2 = 1/K1

 

[hokie4life]

but how come then when we reverse rxns for heats of formation we just make the positive value a negative or vice versa if we reverse the rxns? I was just applying the same logic, is that reverseing to make the value negative only applicable for heats of formation then and for K you do the reciprocal?

thank you 🙂

 

[dantheman2007]

but how come then when we reverse rxns for heats of formation we just make the positive value a negative or vice versa if we reverse the rxns? I was just applying the same logic, is that reverseing to make the value negative only applicable for heats of formation then and for K you do the reciprocal?

thank you 🙂

yes

 

[levyusupov]

The equilibrium constant for Reaction 1 is K. What is the equilibrium constant for Reaction 2?​

Reaction 1: A + 2B...> 2C + D
Reaction 2: 2C + D -->A + 2B
B. –K
C. 1/K​

why is it C and not B? It's the same rxn but backwards so shouldn't the answer be -K? ​

to check yourself and to practice some critical thinking, write the K equation for both of the reactions and make sure they te recipical of each other. it is also useful math practice.

GOOD LUCK !!!

 

[Saber tooth]

To not mix up Heat of Formation with K simply make two colums with rules for each to compair that way when the test comes you'll have a graphic image in your head between the two different rule and wont make a mistake

 

[hokie4life]

very helpful tips...thank you guys! 🙂