Chemical Reactions Take Place…

1. Chemical Reactions Take Place… • Every minute of every day both in and around you • Examples: • Digestion • Photosynthesis • Car batteries-to start your car • Rust

2. Reactions: • One or more substances, the ___________ change into one or more new substances, the __________. • It is written as: • Reactants → Products • The arrow means • “yields” or “reacts to produce” reactants products

3. Chemical Reactions A Balancing Act

4. Explanation: • An explanation was proposed by _____________ who stated in his atomic theory that in a chemical reaction, the way in which atoms are joined together are changed. • As reactants are converted to new products, __________that hold atoms together are __________ and new ones are formed. Dalton bonds broken

5. Explanation: • Daltons atomic theory explains the ____________________________. • Which States: • In any physical or chemical change mass is neither created nor destroyed. • The atoms in the products are the same atoms that were in the reactants, they are just arranged differently. Law of Conservation of Mass

6. Explanation/Practice: left • In a word equation, reactants are written on the ___________ and products are written on the ________. • Write the equation for… • Copper can be produced by heating copper (II) sulfide with oxygen. Sulfur dioxide is also produced. • Water is formed by the explosive reaction between hydrogen and oxygen right

7. Answers • Copper(II)sulfide + Oxygen → Copper + Sulfer dioxide • Hydrogen + Oxygen → Water (Dihydrogen monoxide)

8. Meaning of Chemical Formula Chemical Symbol Meaning Composition H2O One molecule of water: Two H atoms and one O atom 2 H2O Two molecules of water: Four H atoms and two O atoms H2O2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

9. Meaning of Chemical Formula subscript • When a __________is written after the chemical symbol for an element it indicates the___________________. • When a coefficient is written in front of an atom or molecule it indicates the ____________ of that atom or molecule that is present. • If there are subscripts in that atom/molecule they need to be ____________ by the coefficient. # of that element number multiplied

10. Reactants  Products Unbalanced Timberlake, Chemistry 7th Edition, page 164

11. Unbalanced and Balanced Equations H Cl Cl H H Cl H Cl Cl Cl H Cl H H H2 + Cl2 2 HCl (balanced) H2 + Cl2 HCl (unbalanced) reactants products reactants products H H 2 1 2 2 Cl Cl 2 1 2 2 Timberlake, Chemistry 7th Edition, page 167

12. How do we go from Unbalanced to Balanced Equations? • You ____________ change the formula of your atom/ion/molecule! • This means you may not change the ___________ ! • Instead, you may put a coefficient __________ of your atom/ion/molecule to balance the number of atoms after you have ___________ it by the subscript MAY NOT subscript in front multiplied

13. CH4 + 2 O2 CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms Balanced! Timberlake, Chemistry 7th Edition, page 167

14. Balancing Steps 1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients as needed to make #s equal on both sides of the equation. Coefficient  subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!

15. Helpful Tips • Balance one element at a time. • Update ALL atom counts after adding a coefficient. • If an element appears more than once per side, balance it last. • Balance polyatomic ions as single units. • “1 SO4” instead of “1 S” and “4 O”

16. Balancing Example Al + CuCl2 Cu + AlCl3 Al Cu Cl Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 3 3 2  2  6 1 1 1 1 2 3 2  3  6   3

17. More Examples… 4 5 P + O2→ P4O10 H2 + O2→ H2O BaCl2 + H2SO4→ BaSO4 + HCl Cu + AgNO3 → Cu(NO3)2 + Ag CaCO3 + HCl → CaCl2 + H2CO3 2 2 2 2 2 2