The definitive answer is in your lease, as the others have answered.
I'm not a lawyer, so what follows is not legal advice. However . . .
However, often and in general, the answer to your question is: No. The landlord isn't breaking the lease by selling.
What generally applies--unless the lease specifies something different--is that the lease agreement continues to apply both to you and to the new owner.
Example: You signed a 1-year lease on June 1, 2011. Again--assuming the lease doesn't provide otherwise--you've got a valid lease until May 31, 2012. And if the landlord sells the property to someone else before May 31, 2012, that new owner is obligated to fulfill the terms of the existing lease. The lease still runs to May 31; the amount you pay is unchanged.
And--also very important for you--any security deposit you gave to the previous landlord must be returned to you by the NEW landlord. (Sometimes people who purchase rental properties forget to make sure that such deposits are transferred over to them.)
Hope that helps.