Hard examples of physical changes12/26/2023 At the time, chemistry still couldn’t be described as being a true, quantitative science. Lavoisier: Law of Mass ConservationĪntoine Lavoisier was a French nobleman in the 1700s who began to experiment with different chemical reactions. However, there are some important moments in history that have helped to make sense of it. Despite their misguided approach, many early alchemists performed foundational chemical experiments - transforming one substance into another, and so it is difficult to point to a specific date or event as the birth of the idea of an ordered, quantifiable chemical reaction. Alchemists based their approach on Aristotle’s ideas that everything in the world was composed of four fundamental substances - air, earth, fire, and water (Figure 2).įigure 2: Aristotle believed that everything in the world was composed of four fundamental substances - air, earth, fire, and water.Īs such, they proposed, and spent generations trying to prove, that less expensive metals like copper and mercury could be turned into gold. Simple stones, such as those that contained sulfur, seemed to magically burn and otherwise unimpressive minerals were transformed, like the ore cinnabar becoming an enchanting silvery liquid metal mercury when heated. What were these transformations and how were they controlled? These questions could only be answered when the transition from alchemy to chemistry as a quantitative and experimental science took place.īeginning in the early Middle Ages, European and Persian philosophers became fascinated with the way that some substances seemed to “transmute” (or transform) into others. Processes like fermentation, in which sugars are chemically converted into alcohol, have been known for centuries however, the chemical basis of the reaction was not understood. Though chemical reactions have been occurring on Earth since the beginning of time, it wasn’t until the 18th century that the early chemists started to understand them. image ©Cameron Strandberg, Rocky Mountain House In nature, chemical reactions can be much less controlled than you’ll find in the lab, sometimes far messier, and they generally occur whether you want them to or not! Whether it be a fire raging across a forest (Figure 1), the slow process of iron rusting in the presence of oxygen and water over a period of years, or the delicate way in which fruit ripens on a tree, the process of converting one set of chemical substances (the reactants) to another set of substances (the products) is one known as a chemical reaction.įigure 1: A controlled fire in Alberta, Canada, set to create a barrier for future wildfires. In fact, the colossal number of transformations make for a dizzying, almost incomprehensible array of new substances and energy changes that take place in our world every second of every day. While we sometimes associate chemical reactions with the sterile environment of the test tube and the laboratory - nothing could be further from the truth. For the previous version, see this page.)Ĭhemical reactions happen absolutely everywhere. (This is an updated version of the Chemical Reactions module. When energy is released into the surroundings the reaction is said to be exothermic when energy is absorbed from the surroundings the reaction is said to be endothermic Energy plays a crucial role in chemical reactions.Chemical reactions are often accompanied by observable changes such as energy changes, color changes, the release of gas or the formation of a solid.Each type has its own defining characteristics in terms of reactants and products. Chemical reactions can be classified into different types depending on their nature.No energy is created or destroyed, it is conserved but often converted to a different form. Matter is neither created or destroyed, rather it is conserved but rearranged to create new substances. Mass and energy are conserved in chemical reactions.When a substance or substances (the reactants), undergo a change that results in the formation of a new substance or substances (the products), then a chemical reaction is said to have taken place.The steps from a qualitative science to quantitative one, were crucial in understanding chemistry and chemical reactions more completely.
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