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Chemical Equations

Chemical Equations. What are they? What do they tell us? How do we know they are accurate?. Chemical Equations. Chemical Equations are used summarize a chemical reaction Remember, a chemical reaction is any process where a chemical change occurs (and a new substance is formed)

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Chemical Equations

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  1. Chemical Equations What are they? What do they tell us? How do we know they are accurate?

  2. Chemical Equations • Chemical Equations are used summarize a chemical reaction • Remember, a chemical reaction is any process where a chemical change occurs (and a new substance is formed) • Qualitative and quantitative aspects of the reaction can be determined from the chemical equation

  3. Chemical EquationsGeneral Form • Reactants → Products • The substances that undergo the change are referred to as reactants • The substances formed during the reaction are called products • The arrow represents “yields” or “reacts to form” or some equivalent

  4. Chemical EquationsGeneral Characteristics • The equation must represent known facts • All reactants and products must be identified before the equation can be written • The equation must contain the correct formulas for the reactants and products • Correct formulas (esp. transition metals) • Diatomic elements • The Law of Conservation of Mass must be satisfied

  5. Chemical EquationsWord and Formula Equations • Word Equation: reactants and products are represented by words • “reacts to form”, “yields” is represented by the arrow • Formula Equation: reactants and products represented by chemical formulas

  6. Chemical EquationsSymbols Used to Better Represent the Chemical Reaction

  7. Perform the following… • Write a word equation and a formula equation for the chemical reaction that occurs when solid sodium oxide mixes with water to form sodium hydroxide (which is dissolved in water) • Sodium oxide + water → sodium hydroxide solution • Na2O(s) + H2O(l) → NaOH(aq)

  8. Balancing Equations • Conservation of Mass? • Because mass is conserved, the number of each kind of atom must be the same in the reactants and the products • Balance the previous equation • Na2O(s) + H2O(l) → 2 NaOH(aq)

  9. Balancing Equations • A chemical equation must be balanced by adding coefficients in front of formulas and not by changing the subscripts in the formulas • Why?

  10. Write a formula equation and balance it for the following reaction… • Nitrogen gas reacts with hydrogen gas to produce ammonia gas • N2(g) + H2(g) → NH3(g) • N2(g) + 3 H2(g) → 2 NH3(g)

  11. What does this balanced equation tell us? • N2(g) + 3 H2(g) → 2 NH3(g) • 1 molecule of nitrogen (each containing 2 atoms) reacts with 3 molecules of hydrogen (each containing 2 atoms) to form 2 molecules of ammonia (where each molecule contains 1 atom of nitrogen and 3 atoms of hydrogen.) • 1 mole of nitrogen (N2) reacts with 3 moles of hydrogen (H2) to form 2 moles of ammonia (NH3)

  12. Tips for Balancing Equations • Balance the types of atoms that appear in only one reactant and one product. • Balance the remaining types of atoms one at a time. • Balance H and O after most of the other atoms have been balanced. • If polyatomic ions appear on both sides, treat them as is they were single units.

  13. Balancing Equations Practice • Copper metal reacts with a silver nitrate solution to produce silver metal and a copper (II) nitrate solution • Liquid carbon disulfide reacts with oxygen gas to produce carbon dioxide gas and sulfur dioxide gas • Hydrogen peroxide in an aqueous solution decomposes to yield oxygen gas and water.

  14. Balancing Equations Practice • Aqueous solutions of sodium chloride and silver nitrate react to produce a silver chloride precipitate in a sodium nitrate solution • Solid zinc oxide and elemental carbon react to produce zinc metal and carbon dioxide gas • Solid sodium oxide reacts with carbon dioxide gas and water vapor to produce solid sodium bicarbonate

  15. Balancing Equations Practice • The reaction of zinc metal with hydrochloric acid produces a zinc chloride solution and hydrogen gas • Nitric acid reacts with solid magnesium hydroxide to produce aqueous magnesium nitrate and water • Aqueous barium chloride and sulfuric acid are mixed and barium sulfate precipitates from hydrochloric acid

  16. Balancing Equations Practice • Solid zinc sulfide reacts with oxygen gas to produce zinc oxide (the white paste lifeguards use on their noses) and sulfur dioxide gas • Aluminum sulfate and calcium hydroxide are both used in the water purification process. Both are dissolved in water and then added together. When this happens, the two insoluble solids aluminum hydroxide and calcium sulfate are formed. These solids settle and take impurities from the water with them

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