Science 5/8/19 Most spontaneous chemical reactions are exothermic - they release heat and warm up their surroundings: for example: burning wood, fireworks, and alkali metals added to water. E.g. a bonfire, there is a decrease in the energy of the system as energy is released to the surroundings as heat. Spontaneous reactions have no energy. Exothermic. Exothermic – Releases heat. A non spontaneous reaction needs an external energy to pump the reaction this direction. For example, without an external energy source, water will remain water forever. Non Spontaneous reactions need energy. Endothermic (takes in energy). Photosynthesis, plants capture energy from the sun and turn it into glucose. The reactants in a bonfire are wood and oxygen and the product is charcoal. (Spontaneous) Experiment Observations Discussion The indicators that a chemical reaction took place were the color change, it formed a solid (precipitate), and the temperature change. Barium Chloride BaCL2 and Sodium Sulfate Na2SO4 added together. Mixture was rearranged. (Barium Sulfate BaSO4 and Sodium Chloride NaCL.