What are two differences between carbohydrates and lipids?
Lipids have more energy storage capacity than carbohydrates, which is why the body stores energy it doesn't use as fat (lipids). Think about it: if you don't do enough exercise, you have excess energy, and you get fatter.
Lipids are hydrophobic molecules - they hate water and don't dissolve in it, because they don't have much oxygen in them, and carbon doesn't much enjoy the water. Carbohydrates have much more oxygen and so are hydrophillic - that is, they do dissolve in water.
You could also say that carbohydrates can form long chains called polymers, while lipids do not have this ability.