Home > Chemistry > Chemistry 1A Part Deux: Lecture 22 Notes

Chemistry 1A Part Deux: Lecture 22 Notes

Overview

Today is a 51 minute lecture on thermodynamics, just the basics.

Details

Hot objects transfer heat to cold objects until both are the same temperature.

There are physical changes and chemical changes.  Physical changes include an ice cube melting and water freezing.  Chemical changes undergo chemical reactions.

Endothermic if heat in and temperatures is increasing.  Exothermic if heat is out and temperature decreases.

Solid magnesium sulfate is dissolved in water.  The temperatures of the solution rises.  Heat is tranferred….from the solution to the surroundings.

Q = heat = m  cs dT

Heat in is endothermic, heat out is exothermic.  Heat capacity is the heat needed to raise the temperature of one gram of water one degree Celsius, in this case is 1 Calorie.

1 Calorie = 4.184 Joules

q = m Cs dT

Cs is heat capacity per gram

Cp is heat capacity per mole

Diatomic gases have higher heat capacities than noble gases.  Metals tend to have the same heat capacities.  Water has a relative low molar specific heat while ethanol and octane have high molar heat capacities.  Water moderates heat changes by its high heat capacity by gram.  The high heat capacity comes from the polar nature of water and hydrogen bonding.

He does some demos with various types of alcohols, lighting them on fire.  This is at 37 minutes in.  Making things wet can help them from the heat being transferred into them.  The propanol reaction is rather energetic.

Put iron into water.  Find the final water temperature.

Recall Q = m Cs dT

For Iron: 560 grams Fe x .45 J/g K x (100C + 273)

For Water: 560 mL x 1 gram/1mL x (20C + 273) x 4.2 J/g K

Temperature versus time graphs.  Boiling point is the transition from liquid to gas.  Melting point is the transition from solid to liquid.  From an ice cube up to zero, then a horizontal line, up to 100 then horizontal.

Heat of vaporization is the heat need to go from a liquid to a gas.  Heat of fusion is the total heat to melt ice.  It takes more heat to vaporize water.

To create your own calorimeter, burn a cheeto below a vial of water having known temperature and volume.  Then do the calculation.

Heat cheetoo = mass water x specific heat of water x temperature change

Review

PV = nRT

q = m cs dT

K = products/reactants

IGL: point source, random motion, elastic collisions, high temperature, low pressure.

s2, p6, d10, f14

 

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