Tutor profile: John K.

Consider the following reaction: H2(g) + I2(g) --> (reversibly) 2 HI (g). If, at 448C, the equilibrium constant is 50.5, and the initial concentrations are 2.0e-2 mol of HI, 1e-2 mol of H2 and 3e-2 mol of I2 in a 2.00 L container, determine which way the reaction will proceed.

First, determine the initial concentrations in molarity by dividing all the initial moles by the volume of the container: [HI] = 1.0e-2 M [H2] = 5.0e-3 M [I2] = 3.0e-2 M Now, determine Q, the reaction quotient: Q = [HI]^2 / ([H2] * [I2]) = 1.3 Compare Q to K. Since Q < K, and the reaction will proceed so as to establish equilibrium, the concentration of HI must increase. Therefore, the reaction will proceed to the right (products).

Describe and explain the periodic trend(s) related to atomic radii.

Atomic radii tend to increase as you move from top to bottom within a column (group). This is because the principle quantum number n increases; as you add layers to the valence electrons, the electrons have a greater probability of being farther from the nucleus, causing the atom to increase in size.

Six years ago, Nick was three times as old as Erin. Two years later, Nick was twice as old as Erin. How old is Erin now?

Let x be Nick's current age and let y be Erin's current age. Then, six years ago, Nick's age was x-6, and Erin's age was y-6. At that time, Nick was three times as old as Erin, so we can set up the first of two equations: x - 6 = 3(y-6). Distributing the 3 to each term on the left hand side, and rearranging to group all variables on the left hand side, we have: x-2y = -12. Continuing, we know that two years later, Nick was twice as old as Erin. This would be four years ago. We set up an analogous equation: x-4 = 2(y-4), from which we get x-2y = -4. Now, we have two equations and two unknowns. We can solve the system via the elimination technique to find that y = 8. Erin is currently 8 years old.