11. (Ipt ea) The following reaction is exothermic: Predict which direction the e
ID: 696715 • Letter: 1
Question
11. (Ipt ea) The following reaction is exothermic: Predict which direction the equilibrium will shift for of the following stresses placed on the system. (Consider each independently.) Circle the appropriate answer. SHOW the REASON for your decision. 2 H,(g) + 0,(g)2 H,0(g)+ heat a) Removing H,O b) Adding H2 c) Pressure on system is decreased d) Decrease in temperature e) A catalyst is added Shift reverse Shift forward No shift Shift reverse Shift forward No shift Shift reverse Shift forward No shift Shift reverse Shift forward No shift Shift reverse Shift forward No shiftExplanation / Answer
The equilibrium reaction is given as
2 H2 (g) + O2 (g) <=====> 2 H2O (g) + heat
K = [H2O]2/[H2]2[O2] where K is the thermodynamic equilibrium constant and hence, is constant at a particular temperature.
a) When H2O is removed, the numerator decreases; to keep K constant, more H2 and O2 must react to produce H2O. Therefore, the equilibrium shifts forward, producing more H2O.
b) Addition of excess H2 increases the denominator; however, K must remain constant as the temperature is constant. This is possible only when more H2O is produced. Therefore, the equilibrium shifts forward, producing more products.
c) We have 3 moles of gaseous reactants while 2 moles of gaseous products are formed. Hence, there is a change in number of moles of gases by n = -1. When the pressure is decreased, the equilibrium will shift in the direction where pressure is increased. The pressure of a gas is caused by the gas molecules impinging upon the walls of the container of colliding among themselves. The higher the number of molecules, the higher is the pressure. Since the left side contains a higher number of moles of gases, hence, the equilibrium will shift to the left.
d) The reaction produces heat; therefore, we can treat heat as one of the products of the reaction. When the temperature is decreased, the equilibrium will shift in the direction which produces more heat. Since the right side produces heat, the equilibrium will shift to the right.
e) A catalyst alters the rate of both the forward and reverse reactions in equilibrium, but doesn’t alter the position of equilibrium. Therefore, a catalyst has no effect on the system at equilibrium.
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