1. 1 1.D Conservation & Chemical Equations Things that seem to disappear or get used up: Law of Conservation of Matter: matter is neither created nor destroyed; molecules are converted by chemical reactions, but the atoms remain intact Scientific “laws” summarize observations; not the same as a theory

2. Law of Conservation of Mass 2 In any physical change or chemical reaction, mass is conserved. The conservation of mass is easily observed when a change occurs in a closed container.

3. Does the Law of Conservation of Mass Hold? Mg(s) + HCl(aq)  H 2 (g) + MgCl 2 (aq) 3

4. 4 Burning Coal C + O 2  CO 2 1 Carbon atom 1 Oxygen molecule 1 carbon dioxide molecule Balanced chemical equation with physical states: C(s) + O 2 (g)  CO 2 (g) Same number of atoms on reactant and product sides

5. 5 Converting Copper 2 copper atoms + 1 oxygen  2 copper(II) oxide molecule formula units Equation with chemical formulas: 2 Cu(s) + O 2 (g)  2 CuO(s) + subscript coefficient

6. 6 Accounting for Atoms C 3 H 8 + O 2  CO 2 + H 2 O Propane reacts with oxygen to produce carbon dioxide and water Atom inventory: Balanced? Reactant side Product side 3 C atoms1 C atom 8 H atoms2 H atoms 2 O atoms3 O atoms

7. 7 Atom Inventory Practice 1.AgNO 3 2.Sr(OH) 2 3.Al 2 (CO 3 ) 3 4.(NH 4 ) 2 S 5.2 AgNO 3 6.Ca(HCO 3 ) 2 7.4 Ca(HCO 3 ) 2

8. 8 Balancing Chemical Equations CH 4 + O 2  CO 2 + H 2 O CHOCHO 142142 123123 4 2 4 2 4 Fix H atoms first; O atoms appear in two species on the product side (both CO 2 and H 2 O) so balancing O atoms will be harder Check your answer ! ! !

9. 9 C.6 Conservation in the Community The Earth is like a spaceship: the resources “on board” are all that are available Renewable resources can be replenished by natural processes e.g. water, air, fertile soil, plants, animals as long as natural cycles are not disturbed Nonrenewable resources cannot be readily replenished metals, natural gas, coal, petroleum (we are using fuels like petroleum faster than nature is making it) 9

10. 10 How can we avoid depleting nonrenewable resources? The 3 Rs 1.Use less (“source reduction”) 2.Find substitute materials with similar properties; repair or reuse (e.g. used car parts, printer cartridges) 3.Recycle Click for youtube video 10

11. Metal Lifecycle 11 Scrap Steel Steel Making Used Al Cans Car Recycling 11

12. 12 Problems with Recycling? Recycling process costs $, takes energy, may create environmental problems Every American generates 4 lbs trash/day –39% is paper –limited markets for some recycled wastes Waste-to-energy plants may be a solution in the future 12