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Solving Stoichiometry Problems: Balancing Equations and Converting Units

Learn how to balance chemical equations and convert between grams and moles to solve stoichiometry problems. Use coefficients to calculate the number of moles of unknown substances and convert moles into grams.

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Solving Stoichiometry Problems: Balancing Equations and Converting Units

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

  2. 2CH3OH + 3O2 2CO2 + 4H2O grams CH3OH moles CH3OH moles H2O grams H2O 4 mol H2O 18.0 g H2O 1 mol CH3OH x = x x 2 mol CH3OH 32.0 g CH3OH 1 mol H2O Methanol burns in air: If 209 g of methanol are used up in the combustion, what mass of water is produced? molar mass CH3OH molar mass H2O coefficients chemical equation 235 g H2O 209 g CH3OH

  3. 3.8 Other Greenhouse Gases • Methane (CH4) • ~50% of warming due to CH4 • Currently: 1.8 ppm (2000); +1% per year • Sources: fossil fuels, agriculture, biological decay

  4. Nitrous Oxide (N2O) • “Laughing gas”. • Slow increase over past 10 years • 0.31 ppm (2000). • Sources: Fertilizers and deforestation • Leads to ozone depletion. • Soil & CH4 react with N2O  ozone  smog

  5. Tbl. 3.2

  6. Tbl. 3.3

  7. 3.9 Gathering Evidence • Atmosphere is complex • Some factors not understood • Sunspots • Weather patterns • Volcanoes

  8. 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!

  9. Fig.3.24c

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

  11. Disagreements do occur!

  12. Effects? • Ecosystems • Glacier/ice cap retreat • Coral reef damage • Disease spread? • Sea levels • 10-20 cm since 1900 • Severe weather extremes

  13. What can we do? • Gather data/monitor • Reduce fossil fuel dependence • Re-forestation • Better disposal/use of CO2

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