AnnabananannaKam Posted May 21, 2014 Report Share Posted May 21, 2014 Hi all, So i have been assigned a design lab, for Factors Affecting the Equilibrium Reaction in a Solution containing Iron III ions and Thiocyanate Ions. I want to change the temperature, but how do I measure the equilibrium constant? Do I use the Kc value to measure the equilibrium position? How can I obtain the Kc value? I am only in SL and only learnt the products/reactants...... HELP ;( Reply Link to post Share on other sites More sharing options...
sameera95 Posted May 21, 2014 Report Share Posted May 21, 2014 Yes the equilibrium constant is Kc, which is the concentration of products divided by the concentration of reactants. If the Kc value you calculate is <1, the position of equilibrium is on the right hand side (i.e. more reactants), if it is >1 then the position of equilibrium is on the left hand side (i.e. more product) , and if it close to 1, then there are products and reactants in equal proportions. You want to investigate the effect of temperature? Well it's simple enough to explain. I don't know if you've been taught about it (we have to do it at HL), but Le Chatelier's principle which states that any change made to a system in equilibrium, the system will look to oppose that change. So if you increase temperature, the system will decrease the temperature in order to restore the equilibrium. This relates to which reaction (forward or reverse) is the exothermic or endothermic reaction. As an example, let's say your forward reaction is exothermic, so it releases energy. You raise the temperature, so the system wants to decrease it, and it does this by favouring the reaction which will decrease the temperature, which would be the endothermic reaction, in this case the reverse reaction. By favouring the reverse reaction, you therefore end up with more more reactants than products, and this will decrease the value of Kc to <1 (position of equilibrium shifts to the left). If you decrease the temperature, the same will happen but in the opposite direction, and the position of equilibrium shifts to the right, as Kc now becomes >1 For your experiment, you'd have to measure the original concentration (not sure how you're going to measure the concentrations to be honest) of the reactants and products at equilibrium, by taking a sample. Then you'd change the temperature (decrease or increase or both, your choice), let it sit for a while, then take a sample and measure the concentration of that too. You need to have a minimum of 5 different temperatures (other than the control), and I would advise you to take several samples at each temperature to get an average concentration at each temperature. I'm not sure if this method is absolutely the right way to do it, so ask your teacher. I hope this helps though Reply Link to post Share on other sites More sharing options...
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