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21 & 22- Global Energy and atmosphere.docx

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McGill University
CHEM 204
Christopher Barrett

CHEM 204 02/27/13-03/01/13 Lectures 21&22 Martin M. PHGY Tutor Global Energy and Atmosphere Changes Recap: GOALS:1) to see how one can get energy from chemical bonds 2) to learn how to describe Enthalpy changes during reactions 3) to understand how combustion reactions work, and why 1) Energy-releasing reactions trade weaker bonds for stronger bonds 2) During reactions: Δ H R = Δ H ° f products } - Δ H ° {freactants } 3) Combustion reactions add O to a2fuel, and burn to CO and H O2 2 Acid-base theory: the neutralization of an acid by a mineral can be driven forwards OR + backwards by acid itself. CaCO +23 O 3Ca + CO + 3H O 2 2 CaCO +23 O  3a + CO + 3H O 2 2 Note that if we have excess acid, the above reaction will be driven forwards and the rock will dissolve (CO w2ll go in atmosphere). This happens on all old buildings. In our bodies, pH is buffered well but in the environment, CaCO is th3 only buffer and that's not constant! SOx and NOx form in rain too. Acid rain is a big problem that caused the disappearance of many species. A pristine clear lake is actually dead. So H 2ombustion is the cleanest energy, and it has 2.5x thermodynamically better than octane! 1g of H is about 11L of gas and is very explosive. The explosion is even better with O . 2 2 Cons: H i2n't readily available. Recently we can artificially harness the energy from photosynthesis to split a water molecule ("The Artificial Leaf"). Global Energy: Sunlight in Heat out as radiation Distance and luminosity These two numbers are constant. However, some sunlight is actually reflected out, and some of the heat is actually reabsorbed. (Note heat out is constant with T). Reflected sunlight and reabsorbed heat are variables.  Reflection: Different surfaces reflect differently. Oceans reflect 10%, while ice reflects 90%! Reflection is known albedo. Th
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