1.Balance the chemical equation 2.Convert grams of known substances into moles 3.Use coefficients - calculate the number of moles unknown 4.Convert moles into grams Solving Stoichiometry Problems

Methanol burns in air: 2CH 3 OH + 3O 2 2CO 2 + 4H 2 O If 209 g of methanol are used up in the combustion, what mass of water is produced? grams CH 3 OHmoles CH 3 OHmoles H 2 Ograms H 2 O molar mass CH 3 OH coefficients chemical equation molar mass H 2 O 209 g CH 3 OH 1 mol CH 3 OH 32.0 g CH 3 OH x 4 mol H 2 O 2 mol CH 3 OH x 18.0 g H 2 O 1 mol H 2 O x = 235 g H 2 O

3.8 Other Greenhouse Gases Methane (CH 4 ) ~50% of warming due to CH 4 Currently: 1.8 ppm (2000); +1% per year Sources: fossil fuels, agriculture, biological decay

Nitrous Oxide (N 2 O) “Laughing gas”. Slow increase over past 10 years  0.31 ppm (2000). Sources: Fertilizers and deforestation Leads to ozone depletion. Soil & CH 4 react with N 2 O  ozone  smog

Tbl. 3.2

Tbl. 3.3

3.9 Gathering Evidence Atmosphere is complex Some factors not understood – Sunspots – Weather patterns – Volcanoes

Atmospheric variations Inter-related variables – Can’t isolate Data difficult to interpret Currently: Computer modeling Important: Understand model limits How do we know if a model works? Test it!

Fig.3.24c

Computer models – accurate in predicting global temp. changes – temperature is rising – disagreement on the impact increase (O.5 o C over the last century).

Disagreements do occur!

Effects? Ecosystems – Glacier/ice cap retreat – Coral reef damage Disease spread? Sea levels  cm since 1900 Severe weather extremes

What can we do? Gather data/monitor Reduce fossil fuel dependence Re-forestation Better disposal/use of CO 2