Equilibrium, Heat and Le Châtelier Adapted from: Neidig at Lebanon Valley Colleg
ID: 1034310 • Letter: E
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Equilibrium, Heat and Le Châtelier Adapted from: Neidig at Lebanon Valley College and Sipencer a Franklin d and Marshall College Purpose: In this lab, we will explore the effects on a chemical system when its equilibrium is disturbed This can include addition/removal of reactants/products and changes in temperature. We will try to make observations that will coordinate with Le Châtelier's principle Background Information: Most reactions in our lives are not as straightforward as the text books write them. Most reactions favor one side or the other, but usually there is some amount left in the 'unreacted state. An example of this is the synthesis of ammonia. Ammonia is a cleaning agent, but also a major fertilizer. N2(g) + 3H2(g) ? 2 NH(g) The synthesis seems fairly simple: react two gases to form a new gas. However this takes a lot of energy. By utilizing Le Châtelier's principle, a process known as the Haber process was able to optimize this reaction and make the mass production of ammonia possible. The reaction as seen above is only half the story, which is known as the forward reaction (reaction occurring as written from left to right). This reaction can also happen in the opposite directs, or the reverse reaction (reaction occurring from right to left). 2 NH(g) ? N2(g) + 3H2(g) So as some of the ammonia is forming, some ammonia is decomposing back into nitrogen and hydrogen. This is known as a reversible reaction (a reaction that can proceed in either direction). We will write chemical equations that are reversible with a double arrow. N:(g) + 3H(g) 2 NH(g) Systems like this are in a constant state of change. Some ammonias are forming, and some are breaking apart. Once the concentrations of each gas are steady (note the use of the word steady there are still reactions happening, but the rates of them going forward and backwards are equal), we say this has reached the state of equilibrium. At equilibrium, the rates of the forward and reverse reaction are the same. A reaction at equilibrium will stay pretty much the same unless something disturbs it. If a stress is put upon the system will cause a shift in the reaction's attempt to reestablish equilibri can use Le Châtelier's principle to try and predict how the this principle, the reaction will shift forwards or backwards to reduce the stress. The Haber process uses this to increase t equilibrium is stressed and will m um. We reaction will respond. According to he yield of ammonia. By adding more reactant, say nitrogen, the ake more ammonia. We commonly say that this will cause theExplanation / Answer
1.a) H2so4 is a strong dehydrating agent and corrosive. Careless handling will cause skin burns
B) strong oxidising agent, its corrossive, may be allergic to someone. Toxic. Oral intake may be fatal
C) same as all acids HCl is corrossive and causes skin burns
2 a) forward reactions.-*products are formed from reactant molecules.
* its reaction is denoted by forward arrow ?
*equilibrium shifts from left to right in a reversible process.
* Reactant ? product
B) reversible reaction-*priduct formed will give back the reactants under certain conditions. That is reaction takes places in both forward and backward directions.
* reaction is denoted by double headed arrow
C) chemical equilibrium is defined as the condition at which both forward and backward reactions occurs at same rate in a reversible reaction.
D) the reactions involving absorption of energy in the firm of heat are called endothermic reactions
3 (a and b ) addition of Fe3+ to the system causes increase in concentration of reactant molecule Fe3+. According to le chartilier principle, the system in equilibrium try to counter the effect. That means the system will try to reduce its concentration. Hence forward reaction speeds up. More ferric thiocyanate complex forms. So the red colour deepens
( c and d) when silver is added to the system , it reacts with unreacted SCN-ions and form white coloured silver thiocyanate AgSCN. It decreases the concentration of SCN-ions.Hence according to le chartilier principle, the system will try to increase its concentration. Effectively, the backward reaction will occur. That is red colored FeSCN complex will dissociative to give more SCN-ions. Therefore the red colour of the solution fades
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