TEMPERATURE Measure of the average kinetic energy of the molecules.

UNITS FOR TEMPERATURE 1. Fahrenheit Scale (oF) – Fahrenheit temperature scale is a scale based on 32 for the freezing point of water and 212 for the boiling point of water, the interval between the two being divided into 180 parts. The 18th-century German physicist Daniel Gabriel Fahrenheit originally took as the zero of his scale the temperature of an equal ice- salt mixture and selected the value of 98.6 for normal body temperature.

2. Celsius Scale (oC) - is based on 0 for the freezing point of water and 100 for the boiling point of water. Invented in 1742 by the Swedish astronomer Anders Celsius, it is sometimes called the centigrade scale because of the 100-degree interval between the defined points.

3. Kelvin (K) - Kelvin temperature scale is the base unit of thermodynamic temperature measurement in the International System (SI) of measurement. It is defined as 1/ of the triple point (equilibrium among the solid, liquid, and gaseous phases) of pure water. Zero point absolute zero, the theoretical temperature at which the molecules of a substance have the lowest energy. The kelvin has the same magnitude as the degree Celsius.

TEMPERATURE CONVERSION FACTORS

EFFECTS OF HEAT ON MATTER CHANGE IN TEMPERATURE CHANGE IN PHASE CHANGE IN SIZE CHEMICAL CHANGE

CHANGE IN TEMPERATURE – heat energy is converted into kinetic energy of the molecules FACTORS AFFECTING AMOUNT OF HEAT ENERGY (H) NEEDED: 1. TYPE OF MATERIAL (c = specific heat) 2. AMOUNT OF MATERIAL (m = mass) 3. CHANGE IN TEMPERATURE (∆T = final temperature – initial temperature) FORMULA H = cm∆T

Specific heats (c) and molar heat capacities for various substances at 20 C Substancec in J/gm K Molar C J/mol K Aluminum Bismuth Copper Brass Gold Lead Silver Tungsten Zinc Mercury Alcohol (ethyl) Water Ice (-10 C) Granite Glass.84...

CHANGE IN TEMPERATURE What is the amount of heat energy needed to increase the temperature of 100 g of water (c = 4.18 J/g-oC) at 20oC to 50oC? SOLUTION: H = cm∆T = (4.18 J/g-oC)(100g)(50oC-20oC) = J

What is the final temperature (Tf) of 250 g aluminum (c = J/g-oC) if 500 J are added to it? The initial temperature (Ti) of the sample is 25oC. SOLUTION: H = cm∆T ∆T = H = = = = J. cm (0.900 J/g-oC)(250g) = 2.22 oC ∆T = Tf – TiTf = = Ti + ∆T = 25 oC oC = oC

CHANGE IN PHASE – occurred whenever the supplied heat energy is enough to overcome the intermolecular forces of attraction - occurred at specific temperatures (freezing/melting temperatures) and (boiling/condensation temperatures)

CHANGE IN PHASE FACTORS AFFECTING AMOUNT OF HEAT ENERGY (H) NEEDED: 1. AMOUNT OF MATERIAL (m = mass) 2. TYPE OF PHASE CHANGE (dependent on material present) FORMULA: H = Hp mHp is equal to Hf = heat of fusion (melting) -Hf = heat of freezing Hv = heat of vaporization -Hv = heat of condensation

Melting Points and Heat of Fusion Substance Melting point K Melting point °C Heat of fusion (10 3 J/kg) Helium Hydrogen Nitrogen Oxygen Ethyl alcohol Mercury Water Sulfur Lead Antimony Silver Gold Copper

Boiling Points and Heat of Vaporization Substance Boiling point K Boiling point °C Heat of vaporization ( J/g) Helium Hydrogen Nitrogen Oxygen Ethyl alcohol Mercury Water Sulfur Lead Antimony Silver Gold Copper

CHANGE IN PHASE What is the amount of heat energy needed to change 200 g of water at 0oC to ice? (Hf ice = 334 J/g) SOLUTION: H = Hf m = (-334 J/g) (200g) = J Negative sign indicates exothermic reaction

CHANGE IN SIZE – matter increases size whenever heated

CHEMICAL CHANGE – addition of heat favors endothermic reactions; removal of heat favors exothermic reactions.