Elc Posted January 25, 2016 Report Share Posted January 25, 2016 (edited) 7.1 (Equilibrium)Application: determination of the relationship between different equilibrium constants (Kc) for the same reaction at the same temperature. I do not quite get this learning objective. I thought there is only one equilibrium constant (Kc) for the same reaction at the same temperature?What does it mean by relationship between "different equilibrium constants"? What does it want me to know? Edited January 25, 2016 by Elca Reply Link to post Share on other sites More sharing options...
Sandy Posted January 25, 2016 Report Share Posted January 25, 2016 Hey, I read up on this and from what's given in the 2 textbooks that I referred to, this basically means that the value of Kc is different at different points in the reaction. It would be lower than expected if the reaction is incomplete and if its almost complete, it's be higher. For example, it takes 5 minutes for the reaction to reach the equilibrium point. You know the initial concentration of the reactants; you then somehow manage to measure concentrations of reactants as well as products after 2 minutes. Putting these values in the equation, you'll still get a Kc, but this value will be lower than the constant because there are more reactants and less products, comparatively (basically the reaction is still incomplete). I hope that makes it clearer. 1 Reply Link to post Share on other sites More sharing options...
Elc Posted January 25, 2016 Author Report Share Posted January 25, 2016 I initially thought that too, but equilibrium constant, Kc, is the ratio of [product] to [reactant] at equilibrium; everything before that would refers to reaction quotient (Q). The relationship between Q and Kc will tell us the position of equilibrium and the extent it is "complete"; as in, reached equilibrium. Just for clarification, one of the other learning objectives is: (7.1 Equilibrium; understandings) The reaction quotient (Q) measures the relative amount of products and reactants present during a reaction at a particular point in time. Q is the equilibrium expression with non-equilibrium concentrations. The position of the equilibrium changes with changes in concentration, pressure, and temperature. So I think the learning objective I mentioned refers to a different thing, which..uh..I have no idea of. Reply Link to post Share on other sites More sharing options...
Elc Posted January 25, 2016 Author Report Share Posted January 25, 2016 (edited) The reaction quotient Q is what Sandy refers to. As you said, Kc is specified for a reaction at a specified temperature. Different temperature, different Kc. Temperature is the only factor that changes Kc. Whether an increase in temperature increases or decreases Kc depends on whether the reaction is exothermic or endothermic.Yep, got that, that is covered under the last learning objective (Application of Le Châtelier’s principle to predict the qualitative effects of changes of temperature, pressure and concentration on the position of equilibrium and on the value of the equilibrium constant.)Still, though, I don't think that is what it is referring to as the objective specifically states:Application: determination of the relationship between different equilibrium constants (Kc) for the same reaction at the same temperature. Edited January 25, 2016 by Elca Reply Link to post Share on other sites More sharing options...
kw0573 Posted January 25, 2016 Report Share Posted January 25, 2016 You can have equilibrium constant in concentration, pressure, or it can express the forward reaction, or reverse reaction. Reply Link to post Share on other sites More sharing options...
Sandy Posted January 25, 2016 Report Share Posted January 25, 2016 The reaction quotient Q is what Sandy refers to. As you said, Kc is specified for a reaction at a specified temperature. Different temperature, different Kc. Temperature is the only factor that changes Kc. Whether an increase in temperature increases or decreases Kc depends on whether the reaction is exothermic or endothermic.Yep, got that, that is covered under the last learning objective (Application of Le Châtelier’s principle to predict the qualitative effects of changes of temperature, pressure and concentration on the position of equilibrium and on the value of the equilibrium constant.)Still, though, I don't think that is what it is referring to as the objective specifically states:Application: determination of the relationship between different equilibrium constants (Kc) for the same reaction at the same temperature. If you're still unclear, maybe reading the textbooks will help a bit? Which ones do you use? I have oxford and pearson, and both of them explain it well. Maybe you'll understand that better (I mean, they are better at explaining things than me, lol)- refer to ch 7 Reply Link to post Share on other sites More sharing options...
Msj Chem Posted January 26, 2016 Report Share Posted January 26, 2016 (edited) Maybe these videos will help: Manipulating Kchttps://youtu.be/mxZuj2936eM Equilibrium playlist:https://www.youtube.com/playlist?list=PLluIsqNl4jcoWAFhxfQok2pSX4w4Jakxx Edited January 26, 2016 by Msj Chem 1 Reply Link to post Share on other sites More sharing options...
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