Can leftover soup be frozen?

Yes, though some soups freeze better than others. Soups containing cream and/or potatoes don't freeze well, nor do soups containing pasta. During freezing, cream may separate from the soup and curdle. Potatoes and pasta may absorb the broth or sauce and turn mushy, leaving less broth or sauce for consumption. Pasta should be added to soup prior to reheating, after the soup has been defrosted.
 
To freeze leftover soup, first, allow it to cool. Then, transfer it to an airtight freezer-safe container, leaving 1/4-in. headspace so that the broth has room to expand. Frozen soup should be defrosted and consumed within 2-3 months.
 
Source(s):
Reader's Digest "Facts for Freezing Soup"

Canadian Food Inspection Agency "Food Safety Facts on Leftovers"