Heating the egg makes the molecules bounce up and down. Then it slams into the water molecules and all of this moving, break the weak bonds and forms new ones. Combustion takes place as well and this makes a new substance.
When you take out the cake dough, it's not really a cake yet. When you heat it in the oven new bonds are created because of the chemical reaction that occurs. The chemical reaction changes the sticky dough to a fluffy cake.
Cooking a hamburger is a chemical change. One way to know what is a chemical change is you can not reverse the process. When you start cooking the beef, combustion happens. The beef molecules are changed and the new beef or substance is made.
When the chemicals are exploded there is a reaction called combustion that takes place. The chemicals form new ones and releases the energy as sound and light.
When burning wood the carbon the wood has inside mixes with the air to create ashes and smoke. The energy substance changed and it came out as light and heat.