AP CHEMISTRY AIM: ENERGY DO NOW: USING YOUR TEXTBOOKS AND PRIOR KNOWLEDGE OF CHEMISTRY TO ANSWER THE FOLLOWING QUESTIONS: 1.WHAT IS ENERGY? 2.WHAT ARE EXOTHERMIC REACTIONS? 3.WHAT ARE ENDOTHERMIC REACTIONS?

ENERGY Law of Conservation of Energy - Energy can neither be created or destroyed in a chemical reaction but may be converted from one form to another. Energy can be assigned to one of the two classes: potential or kinetic energy.

POTENTIAL ENERGY Potential energy is stored energy or the energy of position. That is, a book 8 feet off the floor has a greater potential energy than a book 2 feet off the floor. Potential energy is important in chemistry because the energy stored in chemical bonds is potential energy. The energy liberated or absorbed in a chemical reaction is similar in many ways to the energy released or needed when a book is raised or lower.

KINETIC ENERGY Kinetic energy is the energy of motion. Particles with high kinetic energy are moving rapidly and those with low kinetic energy of moving slowly. The topic of kinetic energy is often discussed during a lesson on kinetics (rates of reaction). Some forms of energy are heat, light, sound, electrical, chemical, and mechanical energy.

EXOTHERMIC Energy is released in an exothermic process. Any process in which energy is released is an exothermic process. The burning of paper, an explosion, or the condensation of steam are all exothermic process.

ENDOTHERMIC Endothermic - Energy is absorbed in an endothermic process. Any process which requires energy in classified as an endothermic process. The baking of a cake, boiling water, or the of melting ice are all endothermic processes.

UNITS OF ENERGY The unit of energy used in chemistry is the “calorie” or “kilocalorie” (1000 calories). A calorie is the amount of energy needed to change the temperature of 1.0 gram of water, 1.0°C.

HOW DO YOU FIND THE NUMBER OF CALORIES? Since only water (specific heat = 1.00 calorie/gram °C) will be used for energy calculations the equation simplifies to:

PROBLEMS?

PROBLEMS????

HEAT OF FUSION H fus - energy necessary to change one gram of solid into one gram of liquid at its melting point The heat of fusion for ice is calories/gram # calories = mass of solid x H fus

HEAT OF VAPORIZATION H vap - the energy necessary to change one gram of liquid into one gram of vapor at its boiling point. The heat of vaporization for ice is calories/gram # calories = mass of solid x H vap

PROBLEMS???? 1. Calculate the amount of energy needed to melt 200. grams of ice. # calories = mass ice x 80 cal/gram # calories = 200. grams x 80 cal/g # calories = 16,000 calories

PROBLEMS???? 2. How much steam can be prepared by the addition of 2160 calories of heat a sample of water at 100°C? # calories = mass H2O x 540 cal/g # 2160 calories = mass H2O x 540 cal/g mass of H2O = 4 grams H2O

3. How many calories of heat energy are absorbed in raising the temperature of 10. grams of water from 5.0°C to 20°C A.2.5 x 10 2 B.2.0 x 10 2 C.1.5 x 10 2 D.5.0 x 10 1 # calories = mass x specific heat x ∆ T # calories = 10. g x 1.0 cal/ g ∙ °C (20°C - 5°C) # calories = 150 calories = 1.5 x10 2 (C)

4. What is the maximum number of grams of water at 10.°C that can be heated to 30.°C by the addition of 40.0 calories of heat? A.1.0 gram B.2.0 grams C.20 grams D.30 grams # calories = mass x specific heat x ∆ T 40.0 calories = mass x 1.0 cal/ g ∙ °C (30°C - 10°C) 40.0 = 20 x mass Mass = 2.0 grams

5. How many grams of ice can be melted at 0°C by the addition of 4800 calories of energy? A.60 grams B.166 grams C.2.1 grams D.600 grams # calories = mass x heat of fusion 4800 calories = mass ice x 80 cal/ g Mass ice = 4800 calories / 80 cal/g Mass = 60 grams

MEASURE OF THE AVERAGE KINETIC ENERGY OF THOSE MOLECULES. SOME OF THE MOLECULES IN THE SYSTEM ARE MOVING VERY FAST AND SOME ARE MOVING SLOWING OR NOT MOVING AT ALL, BUT THE TEMPERATURE MEASURES THE AVERAGE VELOCITY. TEMPERATURE

That is, the temperature measures the speed at which the molecules move. As the temperature increases, the average velocity increases. If the temperature drops, the average velocity of the molecule slows down.

HEAT Heat flows spontaneously from a body at a high temperature to a body at a lower temperature. Heat flows spontaneously from a body at a high temperature to a body at a lower temperature. Heat is transferred when faster moving, high temperature molecules collide with slower moving, lower temperature molecules. As a result of the collision, the slower moving molecules speed up and thus heat up.

FAHRENHEIT Temperatures are measured by thermometers. The first thermometer was created by Gabriel Fahrenheit ( ). Fahrenheit noticed that the level of some mercury in a tube rose and fell according to how hot or cold it was in his laboratory.

FAHRENHEIT Fahrenheit used his body temperature (100°) and the lowest temperature he could achieve by mixing ice and salt (0°) as the fixed points on his thermometer. The distance between these two points was then divided into 100 equal parts.

CELSIUS Anders Celsius ( ) studied Fahrenheit’s work and devised a thermometer using the boiling point and freezing point of water as his fixed points. The freezing point and boiling points of water are more reproducible than Fahrenheit’s body temperature and freezing point of an ice salt mixture.

CELSIUS Celsius divided the distance between the 0° mark and the 100° mark into 100 equal divisions. Each division equals 1°C. The equation to convert from degrees Celsius to degrees Fahrenheit is °F = (°C X 9/5) + 32

KELVIN William Thomson ( ), known as Lord Kelvin, first suggested a temperature scale which was based on the Celsius scale but does not have negative numbers. He achieved this by setting the lowest possible temperature as “0."

KELVIN The Kelvin scale uses the same fixed points, the boiling point and freezing point of water, and the same divisions as the Celsius scale.

ABSOLUTE ZERO Lord Kelvin’s zero point became known as “ Absolute Zero.” At absolute zero, all molecular motion ceases. Absolute zero is defined as the lowest possible temperature and is believed to be °C.

STANDARD TEMPERATURE Standard temperature is defined as 0°C or 273 K. 0°C is chosen as standard temperature because it is easily obtained and maintained. The sample need only to immersed in a container of melting ice and the temperature is maintained at a constant 0°C.

CONVERTING BETWEEN °C AND °K The equation used to convert from degrees Celsius to degrees Kelvin is: °K = °C Convert 100°C to degrees Kelvin. °K = 100°C = 373 K

PROBLEMS???? Convert from 200 K to °C. °C = 200 K = -73 °C Perform the following conversions: 300 K = ? °C 25°C = ? K 200 °C = ? K 600 K = ? °C

PRESSURE The Pressure is the force exerted on a given area of an object. Gases exert a force on their container by their repeated collision with its sides. This force is dependent upon three factors; the mass of the particles, the number of particles in the container, and their velocity which is related to their temperature.

PRESSURE The most common pressure measured is the atmospheric pressure. Atmospheric pressure is created by the weight of a column of air molecules from the outer limits of our atmosphere to the earth’s surface being pulled towards the surface of the earth by gravity.

PRESSURE A balloon reaches a certain size because the force of the molecules pushing against the inside the balloon equals the atmospheric pressure pressing on the outside surface of the balloon. If either of these forces change, the size of the balloon changes.

MEASURING THE PRESSURE Atmospheric pressure is measured by means of a barometer. A barometer consists of a sealed glass tube filled with mercury and inverted into a container filled with mercury. The mercury in the tube will fall until the weight of the mercury in the tube equals the atmospheric pressure.

UNITS OF PRESSURE The standard unit of pressure is the atmosphere, atm. A standard atmosphere is equivalent to the force exerted by a column of mercury, 760 mm high. Another unit, a mm of Hg, is called “ torr” after Evangelista Torricelli ( ), the inventor of the mercury barometer. 1 atm = 760 mm Hg = 14.7 lb/in2 1 atm = 760 torr = kPa

MERCURY MANOMETER Another method of measuring pressure is with a mercury manometer. Any change of pressure inside the flask changes the level of the mercury in the manometer. Since the liquid inside the manometer is mercury, the change in height measures the change in pressure directly.

WHAT IS THE PRESSURE INSIDE THE FLASK?

STP Standard Temperature and Pressure abbreviated “STP” is defined as a temperature of 273 K (0°C) and one atmosphere (760 torr) pressure. Standard temperature = 0°C or 273 K Standard Pressure = 1 atmosphere or 760 torr

CONCLUSION Complete worksheet with Temperature problems Test is tomorrow All of Chapter 1