The Federal Reserve and Bond Buying

When the Federal Reserve aggressively buys bondsin the open market (QE1, QE2, QE3), what are they attempting to accomplish with respect to the shifts of the AD curve, the equilibrium price and the real national output?

Please explainwhat would happento the AD Curve, the direction of the equilibrium price level and the real national output?

The Fed has recently started trimming their bond purchases and has indicated that it would like to stop this practice soon.

What do you believe would subsequently happen to the AD curve and the real national output?