Chemical Equations and Reactions

1. Chemical Equations and Reactions Describing Chemical Reactions

2. Chemical Reactions • when a substance changes identity • Reactants - original • Products - resulting • Reactants  Products • Law of Conservation of Mass - mass is never created or destroyed, just rearranged • total mass of reactants = total mass of products

3. Chemical Reactions • chemical equation • Written form of a chemical reaction • uses symbols and formulas

4. Hints of Chemical Rxn • heat or light • can also happen with physical changes • gas bubbles • means a gas is product • precipitate • solid is being created • color change

5. Writing Chemical Equations • Most pure elements - write symbol • Diatomic molecules - found in pairs when not bonded to other elements • HOFBrINCl! H2, O2, F2, Br2, I2, N2, Cl2 • Other exceptions • sulfur: S8 • phosphorus: P4

6. yields (produces) reversible Things above arrow show Special requirements: or heat: heated MnO2 or Pt: catalyst 25°C :specific Temp requirement 2 atm: specific Pressure after a formula: (s) solid (l) liquid (aq) aqueous: dissolved in water (g) gas Symbols Used in Equations

7. Coefficients 4Fe(s) + 3 O2(g) 2 Fe2O3(s) • Whole numbers in front of formula • Distributes to numbers of atoms in formula • specifies the number of moles in the reaction • used to balance the equation

8. Word Equations • uses names instead of formulas • helps you to write formula equation

9. Example • Description: Solid sodium oxide is added to water at room temperature and forms sodium hydroxide. • Word Equation: sodium oxide + water  sodium hydroxide • Formula Equation: Na2O + H2O  NaOH

10. Equations cannot tell us: • if the reaction will actually occur • depends on many factors affecting energy • the speed (rate) of the reaction • depends on chemical kinetics • can be altered by temperature, surface area, addition of a catalyst • can be very slow, almost unnoticeably • how the bonding actually changes • formula may not clearly show bonding