Temperature

Temperature Scales Fahrenheit 212 o F 180 o F 32 o F Celcius 100 o C 0 o C Kelvin 373 K 100 K 273 K Boiling point of water Freezing point of water 1 kelvin degree = 1 degree Celcius Notice that 1 kelvin degree = 1 degree Celcius

Temperature Scales Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 136

Temperature Scales Temperature can be subjective and so fixed scales had to be introduced. The boiling point and freezing point of water are two such points. Celsius scale ( o C) –The Celsius scale divides the range from freezing to boiling into 100 divisions. –Original scale had freezing as 100 and boiling as 0. –Today freezing is 0 o C and boiling is 100 o C. Fahrenheit scale ( o F) Mercury and alcohol thermometers rely on thermal expansion

Temperature is Average Kinetic Energy Fast Slow “HOT” “COLD” Kinetic Energy (KE) = ½ m v 2 *Vector = gives direction and magnitude Total kinetic energy is what we call heat. Heat is measured with an instrument called a calorimeter. Temperature is measured with an instrument called a thermometer.

Heat versus Temperature Kinetic energy Fractions of particles lower temperature higher temperature TOTAL Kinetic ENERGY = Heat

Molecular Velocities speed Fractions of particles many different molecular speeds molecules sorted by speed the Maxwell speed distribution

Hot vs. Cold Tea Kinetic energy Many molecules have an intermediate kinetic energy Few molecules have a very high kinetic energy Low temperature (iced tea) High temperature (hot tea) Percent of molecules

Equal Masses of Hot and Cold Water Thin metal wall Insulated box Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 291

Water Molecules in Hot and Cold Water Hot water Cold Water 90 o C 10 o C Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 291

Water Molecules in the same temperature water Water (50 o C) Water (50 o C) Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 291

Temperature vs. Heat Measured with a Calorimeter Total Kinetic Energy Joules (calories) Measured with a Thermometer Average Kinetic Energy o Celcius (or Kelvin) Alike Different A Property of Matter Have Kinetic Energy Heat Different Topic Temperature

Energy

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. (a) Radiant energy(b) Thermal energy (c) Chemical energy(d) Nuclear energy(e) Electrical energy

The energy something possesses due to its motion, depending on mass and velocity. Potential energy Energy in Energy out kinetic energy

Energy Kinetic Energy – energy of motion KE = ½ m v 2 Potential Energy – stored energy Batteries (chemical potential energy) Spring in a watch (mechanical potential energy) Water trapped above a dam (gravitational potential energy) massvelocity (speed) B A C is the ability to do work or produce heat

School Bus or Bullet? Which has more kinetic energy; a slow moving school bus or a fast moving bullet? Recall: KE = ½ m v 2 KE = ½ m v 2 BUSBULLET KE (bus) = ½ (10,000 lbs) (0.5 mph) 2 KE (bullet) = ½ (0.002 lbs) (240 mph) 2 Either may have more KE, it depends on the mass of the bus and the velocity of the bullet. Which is a more important factor: mass or velocity? Why?(Velocity) 2

Potential Energy energy due to the composition or position of an object. (Chemical Potential Energy – energy stored in a substance because of its composition. The potential energy results from the arrangement of the atoms and the strength of the bonds that join them. Stored energy is released when bonds are broken.) Kinetic Energy energy of motion Energy Heat – symbol is q; energy in the process of flowing from a warm object to a cooler one Work – weight lifted through a height

Units of energy calorie where 1 calorie (cal) is the amount of energy needed to raise the temperature of 1 g of water by 1°C. Most common units of energy joule (J), defined as 1(kilogrammeter 2 )/second 2, energy is also expressed in kilojoules (1 kJ = 10 3 J). Units of energy are the same, regardless of the form of energy One cal = J or 1J = cal. metric kilocalorie called a Calorie with a capital “C” sometimes called nutritional calories 1 Calorie = 1000 calories SI

Energy Transformations

ELEMENT hydrogen molecule, H 2 ELEMENT oxygen molecule, O 2 MIXTURE a mixture of hydrogen and oxygen molecules CHEMICAL REACTION if molecules collide with enough force to break them into atoms, a can take place COMPOUND water, H 2 O

2 H 2 O2O2 O2O2 2 H 2 O E E Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

The Zeppelin LZ 129 Hindenburg catching fire on May 6, 1937 at Lakehurst Naval Air Station in New Jersey.

S.S. Hindenburg 35 people died when the Hindenburg exploded. May 1937 at Lakehurst, New Jersey German zeppelin luxury liner Exploded on maiden voyage Filled with hydrogen gas

Hydrogen is the most effective buoyant gas, but is it highly flammable. The disastrous fire in the Hindenburg, a hydrogen-filled dirigible, in 1937 led to the replacement of hydrogen by nonflammable helium.

Exothermic vs. Endothermic

Decomposition of Nitrogen Triiodide

2 NI 3 (s) N 2 (g) + 3 I 2 (g) NI 3 I2I2 N2N2

Direction of Heat Flow Surroundings ENDOthermic q sys > 0 EXOthermic q sys < 0 System Kotz, Purcell, Chemistry & Chemical Reactivity 1991, page 207 System H 2 O(s) + heat  H 2 O(l)melting H 2 O(l)  H 2 O(s) + heat freezing

Conservation of Matter Reactants yield Products

Conservation of Energy in a Chemical Reaction Surroundings System Surroundings System Energy Before reaction After reaction In this example, the energy of the reactants and products increases, while the energy of the surroundings decreases. In every case, however, the total energy does not change. Myers, Oldham, Tocci, Chemistry, 2004, page 41 Endothermic Reaction Reactant + Energy Product

Conservation of Energy in a Chemical Reaction Surroundings System Surroundings System Energy Before reaction After reaction In this example, the energy of the reactants and products decreases, while the energy of the surroundings increases. In every case, however, the total energy does not change. Myers, Oldham, Tocci, Chemistry, 2004, page 41 Exothermic Reaction Reactant Product + Energy

Exothermic Reaction Reactants  Products + Energy 10 energy = 8 energy + 2 energy Reactants Products Energy Energy of reactants Energy of products Reaction Progress -  H Exothermic

Endothermic Reaction Energy + Reactants  Products +  H Endothermic Reaction progress Energy Reactants Products 2 energy + 8 energy = 10 energy +  H Endothermic Energy of reactants Energy of products

Heat Capacity and Specific Heat

Thermal Expansion Most objects e-x-p-a-n-d when heated Large structures such as bridges must be built to leave room for thermal expansion All features expand together COLD HOT Cracks in sidewalk.

Specific Heat

Specific Heat Heat absorbed or released specific heat mass in grams

Specific Heats of Some Substances Specific Heat Substance (cal/ g o C)(J/g o C) Water Alcohol Wood Aluminum Sand Iron Copper Silver Gold

Examples: How much heat is absorbed when a 4.68 g piece of metal experiences a temperature change of 182°C? (Cp =.301 J/g°C) q = m Cp ΔT = (4.68 g)(.301 J/g°C)(182°C) = J =256 J (answer in 3 sig figs)

The temperature of a sample of water increases from 20.0°C to 46.6°C as it absorbs 5650 J of heat. What is the mass of the sample? ΔT = 46.6°C – 20.0°C = 26.6 °C q = m Cp ΔT 5650 J = m (4.184 J/g°C)(26.6°C) 5650 J = m ( J/g) J/g m = g or 50.8 g Examples:

Try: How much heat is released to the surroundings when 200 g of water at 96.0 °C cools to 25.0 °C? Answer = J