1. The main difference between a chemical change and a physical change is that in a physical change, no new substances are formed, and in a chemical change, a new substance is formed. An example of a physical change is freezing water (you can melt it and it still is water.) An example of a chemical change is burning something because the solid that you burn breaks down (because of the heat- SUBLIMATION!!) into many other elements, such as carbon dioxide.
2. The four ways that chemical changes can occur are a solid is formed, a color change happens, a gas is produced (you can tell by bubbles forming), and light, heat, or sound is produced.
3. The Law of Conservation of Mass basically says that mass of an isolated system (which cannot exchange heat, work, or matter with its surroundings) cannot be created or destroyed, but it can be moved around. The law was created by Empedocles, who an ancient Greek philosopher. His idea was "Nothing comes from nothing."
4. Temperature and thermal energy are different because temperature isn't actually energy, but it is a number that is related to energy, or heat ( is related to the average kinetic energy of the molecules in a substance). Thermal energy is ACTUAL energy that is measured in energy units and is the measure of energy in a substance.
5. An exothermic reaction is a reaction that releases energy in the form of heat. An example of this is elephant toothpaste, which reacted by getting very hot. An endothermic (absorbs heat from surroundings) reaction is when an object gets cold (because it is taking in the heat, not releasing it.) An example of this is the experiment that Gabby and I did because the acentric acid and the baking soda reacted to each other by getting very cold.
Cites:
http://www.physlink.com/education/askexperts/ae244.cfm
http://en.wikipedia.org/wiki/Conservation_of_mass
http://zonalandeducation.com/mstm/physics/mechanics/energy/heatAndTemperature/heatAndTemperature.html
http://en.wikipedia.org/wiki/Endothermic_reaction
http://wiki.answers.com/Q/Four_ways_you_can_tell_a_chemical_change_has_taken_place
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