Passage I
A reaction is at equilibrium when the rate of the forward reaction equals the rate of the reverse reaction. At equilibrium, the ratio of product concentration(s) to reactant concentration(s) is the equilibrium constant, K.
Consider the following reaction at equilibrium:
X + Y 
Z
For this reaction, K is given by:
The brackets ([ ]) around the symbol for a substance indicate the equilibrium concentration of the substance.
This reaction was studied in 10 trials. Trials 1-5 were conducted at the same temperature (see Table 1 ) , and Trials 6-10 were conducted at different temperatures (see Table 2).
3. Suppose an additional trial had been conducted at the same temperature at which Trials 1-5 were conducted. If [X] and [Y] had each been 2.00 mol/L, [Z] would most likely have been:
Your Answer is
Correct Answer is C
Explanation
According to table 1, at this reaction temperature, K is all 0.10, put it into the formula to calculate 0.10=[Z]/2☓2, and get [Z]=0.40