1. Chemical reactions

2. Chemical reactions happen all the time. They can be shown by a general equation: Reactants  Products The same amount of chemicals must be present on both sides of the reaction. The reactants are the chemicals that react together. The products are the new chemicals that are made.

3. What do the numbers mean? SO 2 – 1 sulphur – 2 oxygen MgCO 3 – 1 magnesium – 1 carbon – 3 oxygen

4. Identifying atoms CompoundElement N o of atoms Element N o of atoms Salt (NaCl)Sodium1Chlorine1 Carbon dioxide (CO 2 )CarbonOxygen Water (H 2 O)HydrogenOxygen Methane (CH 4 )CarbonHydrogen Hydrogen sulphide (H 2 S) HydrogenSulphur Calcium carbonate (CaCO 3 ) CalciumCarbon Oxygen

5. Identifying atoms CompoundElement N o of atoms Element N o of atoms Salt (NaCl)Sodium1Chlorine1 Carbon dioxide (CO 2 )Carbon1Oxygen2 Water (H 2 O)HydrogenOxygen Methane (CH 4 )CarbonHydrogen Hydrogen sulphide (H 2 S) HydrogenSulphur Calcium carbonate (CaCO 3 ) CalciumCarbon Oxygen

6. Identifying atoms CompoundElement N o of atoms Element N o of atoms Salt (NaCl)Sodium1Chlorine1 Carbon dioxide (CO 2 )Carbon1Oxygen2 Water (H 2 O)Hydrogen2Oxygen1 Methane (CH 4 )CarbonHydrogen Hydrogen sulphide (H 2 S) HydrogenSulphur Calcium carbonate (CaCO 3 ) CalciumCarbon Oxygen

7. Identifying atoms CompoundElement N o of atoms Element N o of atoms Salt (NaCl)Sodium1Chlorine1 Carbon dioxide (CO 2 )Carbon1Oxygen2 Water (H 2 O)Hydrogen2Oxygen1 Methane (CH 4 )Carbon1Hydrogen4 Hydrogen sulphide (H 2 S) HydrogenSulphur Calcium carbonate (CaCO 3 ) CalciumCarbon Oxygen

8. Identifying atoms CompoundElement N o of atoms Element N o of atoms Salt (NaCl)Sodium1Chlorine1 Carbon dioxide (CO 2 )Carbon1Oxygen2 Water (H 2 O)Hydrogen2Oxygen1 Methane (CH 4 )Carbon1Hydrogen4 Hydrogen sulphide (H 2 S) Hydrogen2Sulphur1 Calcium carbonate (CaCO 3 ) CalciumCarbon Oxygen

9. Identifying atoms CompoundElement N o of atoms Element N o of atoms Salt (NaCl)Sodium1Chlorine1 Carbon dioxide (CO 2 )Carbon1Oxygen2 Water (H 2 O)Hydrogen2Oxygen1 Methane (CH 4 )Carbon1Hydrogen4 Hydrogen sulphide (H 2 S) Hydrogen2Sulphur1 Calcium carbonate (CaCO 3 ) Calcium1Carbon1 Oxygen3

10. Now try these… How many atoms of each element are in the following molecules? 1. H 2 SO 4 2. Ca(OH) 2 3. NaCl 4. (NH 3 ) 3 P0 4 5. 3H 2 O 6.Al 2 (CO 3 ) 3 See CH10Mod03PP for answers

11. Representing reactions When reactions occur the products are turned into reactants. This is written as a balanced equation. We also might need to be able to draw this as the molecules, and in more detail as the atoms involved.

12. What is balanced in a chemical equation? Three things are balanced in a chemical equation: 1. Atoms 2. Mass 3. Charge More on this in Module 3