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Chemical Reactions

Chemical Reactions. What do you notice about the two pictures?. A. Chemical reactions are changes of one or more substances into one or more new substances. Reactants  Products (produce) Reactants are the substances that combine or change. Products are the result of the reaction.

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Chemical Reactions

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  1. Chemical Reactions

  2. What do you notice about the two pictures?

  3. A. Chemical reactions are changes of one or more substances into one or more new substances. Reactants  Products (produce) • Reactants are the substances that combine or change. • Products are the result of the reaction.

  4. B. The law of conservation of mass – in a chemical reaction, matter isnot created or destroyed. The mass of the candles and oxygen before burning . . . Is exactly equal to The mass of the remaining candle and gaseous products.

  5. According to the law of conservation of mass, what is known about mass in the reaction? 64g 200g = 160g ? 104g = 264g 264g – 160g = In the reaction above, how much zinc was present in the zinc carbonate? _

  6. Practice conservation Problems 130 g NaN3 + 88.0g N2 + ?g Na 223.4 g Fe + 128.0 g O2?g Fe2O3 ?g NH4NO3 18.0 g H2O + 22.0 g N2O 44.0 g C3H8 + 112.0 g O2 132.0 g CO2 + ?g H2O 42g 351.4g 40.0g 24.0g

  7. C. Chemical equations use chemical formulas and symbols to describe a chemical reaction. • Chemical Symbols represent the elements. • Chemical formulas express the ratio of elements in compounds. • Subscripts – numbers representing the atoms of an element in a compound. • Parenthesis – used to represent polyatomic ions within a compound.

  8. Table 1 Symbols Used In Chemical Equations  produces, yields, or forms. + plus (s) Solid (l) Liquid (g) Gas (aq) Aqueous – dissolved in water

  9. Analyze a Chemical Equation Let’s take close look at a chemical equation. 2Na + Cl2 2NaCl Reactants Products First, you should notice that the equation is broken into two parts with an arrow.The arrow represents the chemical reaction. The “ingredients” on the left side of the equation are called the Reactants The “results” on the right side of the equation are called the Products

  10. Analyze a Chemical Equation • Identify the reactants and the products in the following reactions. N2 + 3H2 2NH3 BaCO3 BaO + CO2 MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O Reactants Products

  11. Coefficients – numbers in equations which represent the number of units of each substance in a reaction. Subscripts – number that represent the ratio of atoms in the formula of that substance. 2Na + Cl2 2NaCl Coefficients Subscripts The subscripts in this equation tell us… Na is in elemental form.2 Cl atoms are bonded to form a molecule of chlorine gas.1 Na is bonded to 1 Cl to make a molecule of sodium chloride. Coefficients tell the number of atoms or molecules that are required for the reaction. Coefficients are the amounts of the reactants and products. The coefficients in this equation tell us…Two sodium atoms will react with One chlorine molecule to produce Two molecules of sodium chloride. The small numbers following the chemical symbols are called Subscripts.(Subscripts of one are not written out.) Subscripts tell the number of atoms that are bonded together to makea single molecule of a substance. They determine the substance itself. You probably noticed the numbers associated with chemical formulas for the reactants and the products. The large numbers in front of the formulas are called Coefficients. (Coefficients of one are not written out.)

  12. Analyze a Chemical Reaction with it’s EquationNiCl2(aq) + 2NaOH(aq)  Ni(OH)2(s) + 2NaCl(aq) • A white precipitate of nickel(II) hydroxide forms when sodium hydroxide is added to a green solution of nickel(II) chloride. • Sodium chloride, the other product formed is in the solution.

  13. Let’s take another look at that chemical reaction. NiCl2 + 2NaOH Ni(OH)2 + 2NaCl Reactants Products First, you should notice that the equation is broken into two parts with an arrow.The arrow represents the chemical reaction. The “ingredients” on the left side of the equation are called the Reactants The “results” on the right side of the equation are called the Products

  14. Let’s take another look at that chemical reaction. NiCl2(aq) + 2NaOH(aq)  Ni(OH)2(s) + 2NaCl(aq) Coefficients Subscripts Subscripts tell the number of atoms that are bonded together to make one unit of the substance. In this equation 2 chloride Ions in NiCl2 and 2 OH- Ions in Ni(OH)2 The coefficients in this equation tell us…One molecule of nickle chloride react with Two molecules of sodium hydroxide to produce One molecule of nickle hydroxide and Two molecules of sodium chloride. The small numbers following the chemical symbols are called Subscripts. (Subscripts of one are not written out.) Coefficients tell the number of atoms or molecules that are required for the reaction. Coefficients are the amounts of the reactants and products. You probably noticed the numbers associated with chemical formulas for the reactants and the products. The large numbers in front of the formulas are called Coefficients. (Coefficients of one are not written out.) Back

  15. Analyze a Chemical Equation • What do the chemical equations below tell you? N2 (g) + 3H2 (g)  2NH3 (NH3 is Ammonia) 2MgO + Si  2Mg + SiO2 1 molecule of nitrogen reacts with 3 molecules of hydrogen to form 2 molecules of ammonia. Nitrogen and hydrogen molecules are each formed from 2 atoms bonded together. Ammonia is formed from 1 N atom bonded to 3 H atoms. 2 molecules of Magnesium Oxide (each with 1Mg bonded to 1 O) react with 1 atom of silicon to form 2 atoms of magnesium and 1 molecule of silicon dioxide (having 1 Si bonded to 2 O)

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