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Understanding Chemical Reactions: Conservation of Mass and Writing Equations

Chapter 21, Section 1 delves into chemical changes and reactions, defining reactants and products. It highlights Antoine Lavoisier's groundbreaking contributions to chemistry, notably the law of conservation of mass, which states that the total mass of reactants equals that of products. His experiments with mercury(II) oxide demonstrate this principle. The chapter also covers writing chemical equations to describe reactions accurately using symbols and coefficients. Furthermore, it addresses the corrosion of metals like iron, copper, and aluminum when exposed to atmospheric conditions.

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Understanding Chemical Reactions: Conservation of Mass and Writing Equations

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  1. Chapter 21 Section 1 Chemical Changes

  2. Describing Chemical Reactions • Chemical reaction – a process in which one or more substances are changed into new substances • Reactants – Substances that react • Product - new substance that is produced

  3. Conservation of Mass • Antoine Lavoisier established that the total mass of the products always equals the total mass of the reactants • Mass of candle and oxygen before burning = mass of remaining candle and gaseous products

  4. Lavoisier’s Contribution • He placed a carefully measured mass of solid mercury (II) oxide into a sealed container • He heated it and the red powder changed into a silvery liquid (mercury metal)and a gas was produced (oxygen) • The combined masses of the liquid mercury and gas were exactly the same as the mass of the red powder he had started with.

  5. Father of Modern Chemistry and Nomenclature • Lavoisier is known for his more accurate explanation of the conservation of mass and for describing combustion • He also developed the system of naming substances based on their composition that we still use today.

  6. Writing Equations • Chemical equation = a way to describe a chemical reaction using chemical formulas and other symbols • NiCl2(aq) + 2 NaOH(aq) Ni(OH)2(s) + 2 NaCl(aq)

  7. Unit Managers • Atoms are neither made nor lost in a chemical reaction, only rearranged • Coefficients = represents the number of units of each substance taking part in a reaction • Allows scientists to add the correct amount of reactants and tell them exactly how much product will form

  8. Metals and the Atmosphere • Iron corrodes as it reacts with air & moisture, forming hydrated iron (III) oxide & causing serious damage • Copper is another metal that corrodes when it is exposed to air, forming a blue-green coating called a patina • Aluminum also reacts with oxygen in the air to form aluminum oxide (protects)

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