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Chemical Reactions: An Introduction Chapter 6

Chemical Reactions: An Introduction Chapter 6. 6.1 Evidence of Chemical Reactions. Chemical reactions involve the rearrangement and exchange of atoms to produce new compounds. Evidence: (fig 6.1, 6.2, 6.3) color change, precipitate formation, gas bubbles, flames, heat release, cooling, light

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Chemical Reactions: An Introduction Chapter 6

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  1. Chemical Reactions:An IntroductionChapter 6

  2. 6.1 Evidence of Chemical Reactions • Chemical reactions involve the rearrangement and exchange of atoms to produce new compounds. • Evidence: (fig 6.1, 6.2, 6.3) • color change, precipitate formation, gas bubbles, flames, heat release, cooling, light • new odor, permanent new state

  3. 6.2 Chemical Equations • A chemical reaction is a chemical change involving a rearrangement of the ways in which atoms are grouped. • A chemical equation is a shorthand way of describing a reaction. It is written in the following form: Reactants  Products Ex: CH4 + O2  CO2 + H2O The arrow indicates the direction of the change and is read as “yields” or “produces”. • A reactant is a starting substance in a chemical reaction, whereas a product is a substance resulting from a chemical reaction.

  4. Chemical equations provide information about the reaction: • The formulas of reactants and products. • The states of reactants and products. • Physical states are shown by symbols used after a chemical formula: (g) = gas; (l) = liquid; (s) = solid (aq) = aqueous, dissolved in water • The numbers of reactant and product molecules that are required (when balanced). • Used to predict the amount of product produced in a chemical reaction based on amount of reactants.

  5. Law of Conservation of Mass • In chemical reactions matter cannot be created or destroyed. • The number and type of atoms in the reactants are still present in the products, they’ve only been rearranged. • The total mass of the reactants will equal the total mass of the products. • Elements are not transmuted (changed) in a reaction. • Equations are balanced to ensure compliance with the law.

  6. 6.3 Balancing Chemical Equations • Use proper formulas for each reactant and product. • A balanced chemical equation: • obeys the Law of Conservation of Mass. • shows equal numbers of atoms of each element on reactant side as on product side. • shows the relationship between the relative numbers of molecules/formula units/atoms of reactants and products. • The formulas of reactants or products can never be changed in balancing a chemical equation. Equations are balanced by changing the number of molecules/formula units/atoms in the reaction. • See page 162 in text on how to write and balance equations. • See specific examples in text and class

  7. Writing chemical equations. You must be able to read a description of a chemical reaction and write a balanced chemical equation from the names of the compounds. For example: try writing balanced chemical equation for problems 17, 19 and 21 on page 167 of your text. You can, of course, practice writing chemical equations for the even-numbered problems and checking your answers in the Appendix (green tab). It is expected that you can write chemical equations from their descriptions on the test.

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