lecture 05 2010

lecture 05 2010 - 24 A few parting thoughts on...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
24 A few parting thoughts on thermochemistry On thermochemistry: The enthalpies of formation of the elements in their standard states are zero. On carbon-based fuels : the problem with combustion of fossil fuels comes CO 2 production. CO 2 can be removed from the atmosphere by photosynthesis. Carbon can be fixed in the leaves of plants at the rate of about 200 – 400 g/ (m 2 – yr), or about 0.5 to 1.0 grams per m 2 of leaf cover per day. However, the conversion of this atmospheric CO 2 to fossil fuels take millions years, and so is not carbon-neutral. However, replacing fossil fuels with biomass, in which the recycling time is as short as one year (for cereal grains, switch grass, etc), is much closer to carbon neutral. Of course there is a carbon footprint for the machinery and fertilizers to grow and harvest the biomass. Hydrogen is an important alternative, provided the primary energy source for producing hydrogen is not fossil fuel based – more on this later Entropy and Spontaneous Processes The First Law places the constraint of energy conservation on all physical processes. Therefore, it does provide us with constraints on what physical processes can happen. But, not all such processes actually do occur. Examples: A mixture does not spontaneously unmix A gas that expands from a smaller volume into a larger volume does not spontaneously retreat to the smaller volume. Heat does not flow spontaneously from a cold object to a hot object. Scientists in the 19 th century who analyzed such processes determined that a quantity called entropy behaved in a predictable way in processes that appeared to proceed in a spontaneous, non-reversible way.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
25 Let’s motivate the discussion by considering what I’ll call configurational microstates. Take two particles,
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

Page1 / 5

lecture 05 2010 - 24 A few parting thoughts on...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online