What energy changes is taking place in a blender

Electrical energy is supplied to the blender. This is converted into kinetic energy to turn the blades that blend the food, so energy is transferred from electrical to kinetic. This is the useful energy change that we most want to happen.
However, not 100% of the electrical energy is transferred to kinetic energy. Some of the electrical energy is converted to sound energy (which is why blenders are noisy) and some is converted to heat (which is why you shouldn't leave them running for ages). These are less useful energy changes as they do not help to blend the food.