1 / 10

Lecture 23: Heat

Lecture 23: Heat. Internal Energy Heat Specific Heat Latent Heat Phase Diagrams. Internal Energy. Energy of all molecules including: Random motion of individual molecules <K tr > = 3/2 k T for ideal gas Vibrational energy of molecules and atoms

karas
Download Presentation

Lecture 23: Heat

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 23:Heat • Internal Energy • Heat • Specific Heat • Latent Heat • Phase Diagrams

  2. Internal Energy • Energy of all molecules including: • Random motion of individual molecules • <Ktr> = 3/2 k T for ideal gas • Vibrational energy of molecules and atoms • Chemical energy in bonds and interactions • DOES NOT INCLUDE • Macroscopic motion of object • Potential energy due to interactions w/ other objects

  3. Heat • Definition: Flow of energy between two objects due to difference in temperature • Note: similar to WORK • Object does not “have” heat (it has energy) • Units: calorie • Amount of heat needed to raise 1g of water 1ºC • 1 Calorie = 1000 calories = 4186 Joules

  4. Specific Heat • Heat adds energy to object/system. • If system does NO work then: • Heat increases internal energy.Q = DU • Heat increases temperature! • Heat required to increase temperature depends on amount of material (m) and type of material (c). • Q = c m DT • Q = heat • c = specific heat • m = mass • DT = change in temperature

  5. Specific Heat: Ideal Gases • Monatomic Gas (single atom): • All energy is translational kinetic energy. • At constant volume, work = 0. • Q = DKtr = 3/2 nRDT • CV = 3/2 R = 12.5 J/(K mole) • Diatomic Gas (two atoms): • Also have rotational energy. • CV = 5/2 R = 20.8 J/(K mole)

  6. steam: temp rises water changesto steam(boils) water: temp rises T 100oC Latent Heat Q added to water Latent Heat • As you add heat to water, the temperature increases for a while, then it remains constant, despite the additional heat! • Q = m L • Latent Heat: L [J/kg] is heat which must be added (or removed) for material to change phase (solid-liquid or liquid-gas).

  7. Summary • Heat is FLOW of energy • Heat will increase internal energy. • Specific Heat • Q = c m Dt • Monatomic IDEAL Gas: CV = 3/2 R • Diatomic IDEAL Gas: CV = 5/2 R • Latent Heat • Heat associated with change in phase • Q = m L

  8. Example • How much heat is needed to change 1.8 grams of ice at -10ºC to steam at 100ºC? • cice = 2.100 J/g/ºC • cwater = 4.186 J/g/ºC • Lfusion = 333.7 J/g • Lvaporization = 2256 J/g We will need to use both equations for this problem: Q = c m Tto raise the temperature of the ice from -10ºC to 0ºC Q = m Lto melt the ice to water Q = c m Tto raise the temperature of the water from 0ºC to 100ºC Q = m Lto boil the water to steam

  9. Example • How much heat is needed to change 1.8 grams of ice at -10ºC to steam at 100ºC? • cice = 2.100 J/g/ºC • cwater = 4.186 J/g/ºC • Lfusion = 333.7 J/g • Lvaporization = 2256 J/g Set up an expression for the total heat needed: Q = cice m Tice + m Lfusion + cwater m Twater + m Lvaporization Solve for the total heat needed: Q = 37.8 J + 600.66 J + 753.48 J + 4060.8 J = 5452.74 J

  10. Phase Diagrams

More Related