Q and speed of reaction

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Keya Jonnalagadda 1A
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Joined: Mon Jun 17, 2019 7:24 am

Q and speed of reaction

Postby Keya Jonnalagadda 1A » Fri Jan 10, 2020 6:56 am

Does Q affect the speed of the forward and reverse reactions in an equilibrium reaction? For example, does the forward reaction proceed more rapidly when Q is greater than K?

Justin Quan 4I
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Joined: Sat Sep 14, 2019 12:17 am

Re: Q and speed of reaction

Postby Justin Quan 4I » Fri Jan 10, 2020 8:26 am

Q is the reaction quotient. If Q>K, then the reaction will proceed backwards (reverse reaction), and if Q<K then the reaction will proceed forward. So if Q is greater than K, that means there are more product than reactant, and the reaction will shift left.

Tyler Angtuaco 1G
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Joined: Wed Sep 11, 2019 12:16 am

Re: Q and speed of reaction

Postby Tyler Angtuaco 1G » Fri Jan 10, 2020 8:27 am

Q itself is just a calculation made from the current concentrations or pressures of products and reactants during some point of the reaction. Thus, it does not impact the speed of the reaction. However, you can make observations about the direction a reaction will proceed based on the comparison between Q and K. If Q<K, then more products are needed to reach equilibrium so the forward reaction is favored. Conversely, if Q>K, then the reaction there are too many products for the amount of reactants and the reverse reaction is favored. If you are considering the latter concept (Q>K) with a real world example, such as chemical reactions in a river, and wonder if this means the reaction produced more products than what is necessary for equilibrium, it didn't. It just happens to be that whatever you designated as "product" is actually the reactant in the current reaction (reverse reaction) and is producing more product (what you labeled as "reactant") to reach equilibrium. This is not a new concept, but rather an explanation of the reverse reaction.

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Re: Q and speed of reaction

Postby CosetteBackus_4F » Fri Jan 10, 2020 11:55 am

Q measures the ratio of the concentrations of products and reactants, but is not affected by speed, only concentrations, temperature, and pressure.

Louise Lin 2B
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Joined: Sat Aug 17, 2019 12:15 am

Re: Q and speed of reaction

Postby Louise Lin 2B » Fri Jan 10, 2020 5:18 pm

Q is only the constant calculated from the ratio between the products and reactants at some point in time during the reaction before it reaches equilibrium. It does not actually tell us the speed at which the reaction takes place.

Helen Struble 2F
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Joined: Sat Aug 24, 2019 12:17 am

Re: Q and speed of reaction

Postby Helen Struble 2F » Sun Jan 12, 2020 3:27 pm

In the same way that K does not tell us about how quickly a reaction reached equilibrium, Q only tells us which direction a reaction will proceed, not how quickly. This is because Q is calculated from the instantaneous pressures or concentrations. Since it's from one instant, we cannot infer any information about speed.

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