[Music] studying chemical reactions helps us understand and explain how the natural world works chemical reactions turn that slice of pizza you ate into fuel for your body make dazzling firework displays on the 4th of July or can even stop cancer cells from multiplying in a synthesis reaction or combination reaction two or more substances combined to form a single product you can use the generalized formula a plus B yields a B to predict the products of a synthesis reaction here aluminum is mixed with iodine aluminum is covered with an oxide layer which protects it from constantly reacting however a little water removes that protective layer and enables the reaction to take place initially you see the purple iodine gas released then aluminum sparks and finally a product aluminum iodide photosynthesis is fundamental to life on Earth through the synthesis reaction plants produce glucose which they use for energy and oxygen without this process we wouldn't have food to eat or oxygen to breathe a decomposition reaction is the opposite of synthesis during decomposition one substance breaks down into two or more separate substances the generalized formula is a B yields a plus B here we have hydrogen peroxide with a catalyst added if left alone it would decompose over time but adding a catalyst accelerates its decomposition into water and oxygen gas during a car accident airbags to point under 50 milliseconds using a decomposition reaction upon impact the solid sodium azide decomposes and inflates the airbag a combustion reaction occurs when a substance reacts with oxygen to produce energy in the form of heat or light when combustion occurs with an organic compound the products are almost always co2 and h2o here we infused bubbles with methane gas when heat is added it triggers the combustion of methane our final products are carbon dioxide and water vapor without combustion we wouldn't be able to enjoy summer BBQs the combustion of propane is the most common reaction used to ignite your grills the heat produced from the reaction allows us to cook up our hamburgers and hotdogs a single replacement reaction also called a single displacement reaction occurs when one element replaces another element in a compound the generalized formula is a plus B C yields a C plus B here we placed a copper wire in a silver nitrate solution copper is more reactive than silver so it replaces the silver in the silver nitrate our products are copper to nitrate and silver crystals you can see the silver crystals beginning to accumulate on the wire and the solution turned blue from the dissolved copper thermite reactions a type of single replacement are crucial for maintaining railway tracks the intense energy generated during the reaction produces molten metal which is then used to fill gaps between tracks in a double replacement reaction also called a double displacement reaction the positive ion of one compound replaces the positive ion of the other to form two new compounds one of those products is always a gas water or precipitate the generalized formula is a B plus C D yields a D plus C B when potassium iodide is added to lead ii nitrate the potassium and lead swap places you can observe the yellow lead 2 iodide precipitating from the potassium nitrate eating a huge meal can put pressure on the ring of muscle that keeps stomach acids from moving in the wrong direction so juices from your last meal may come back to haunt you in the form of heartburn luckily antacids help soothe the burn during this double replacement reaction the calcium hydroxide from the antacid neutralizes stomach acid imagine a universe without chemical reactions the ingredients in our pizza will stop growing our skies would go dark and you and I would cease to exist so let us appreciate the diversity of reactions that exist in our universe and make life as we know it possible