Introduction to Physical Science

Monday, Wednesday, Thursday

Tom Burbinetomburbine@astro.umass.edu

Quiz• Temperature• T(K) = T(oC) + 273.15• Three laws of thermodynamics• Absolute zero• Entropy• Specific heat capacity • Q = c m ∆T• Properties of ice and water• Thermal expansion

Entropy• Entropy is the measure of how energy spreads to

disorder in a system

Entropy

• Entropy is a measure of the "multiplicity" associated with the state of the objects.

• If a given state can be accomplished in many more ways, then it is more probable than one which can be accomplished in only a few ways.

Specific Heat Capacity

• Specific heat capacity of any substance is defined as the quantity of heat required to change the temperature of a unit mass of the substance by 1 oC

For example

• The filling of hot apple pie can be very hot while the crust is not. The filling and crust have different specific heat capacities.

• It takes a longer time to heat a pot of water to its boiling temperature than to heat an equal mass of iron to the same temperature.

Water

• Water can absorb a great amount of heat for small increases in temperature

• That is why water is useful in cooling systems

• Q = c m ∆T• Q is the quantity of heat• c is the specific heat of the substance• m is the mass• ∆T is the temperature change

• specific heat of water is 1.0 cal/(g ∙oC) or 4.186 J /(g ∙oC)

Example• You mix 100 g of water at 25oC with 75 g of water at 40 oC• What is the final temperature?

• Heat gained by cool water = Heat lost by warm water• c m1 ∆T1 = c m2 ∆T2

• c (100 g)(T-25) = c (75g) (40-T)• 100T – 2500 = 3000 – 75T• T = 31.4 oC

Proton Alpha Helix

• Temperature reflects the average total kinetic energy of the particles

• Heat is the transfer of thermal energy; it flows from regions of high temperature to regions of low temperature.

• Thermal energy is stored as kinetic energy and, in molecules and solids, also as potential energy in the modes of vibration

Thermal Expansion• As the temperature of a substance increases, its

molecules move faster and move farther apart

• Most substances expand when heated and contract when cooled

• Ice is the only known non-metallic substance to expand when it freezes.

0 oC1 oC2 oC3 oC4 oC

Any Questions?