A P C H E M I S T RY

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 canneither be created or destroyed in a chemicalreaction but may be converted from one form toanother.

• Energy can be assigned to one of the twoclasses: potential or kinetic energy.

POTENTIAL ENERGY

• Potential energy is stored energy or the energyof position. That is, a book 8 feet off the floorhas a greater potential energy than a book 2 feetoff the floor. Potential energy is important inchemistry because the energy stored in chemicalbonds is potential energy.

• The energy liberated or absorbed in a chemicalreaction is similar in many ways to the energyreleased or needed when a book is raised orlower.

KINETIC ENERGY

• Kinetic energy is the energy of motion.Particles with high kinetic energy are movingrapidly and those with low kinetic energy ofmoving slowly. The topic of kinetic energy isoften 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 anexothermic process. Any process in which energy is released is an exothermic process.

• The burning of paper, an explosion, or thecondensation of steam are all exothermicprocess.

ENDOTHERMIC

• Endothermic - Energy is absorbed in anendothermic process. Any process whichrequires energy in classified as an endothermicprocess.

• The baking of a cake, boiling water, orthe 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 tochange 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?

amount of energy = 1500 calories

PROBLEMS????

HEAT OF FUSION

• Hfus - energy necessary to change one gram of solid into one gram of liquid at its melting point

• The heat of fusion for ice is 79.72 calories/gram

• # calories = mass of solid x Hfus

HEAT OF VAPORIZATION

• Hvap - 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 539.4

calories/gram

• # calories = mass of solid x Hvap

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 102 B. 2.0 x 102 C. 1.5 x 102 D. 5.0 x 101

# 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 x102 (C)

4. What is the maximum number of grams of waterat 10.°C that can be heated to 30.°C by theaddition of 40.0 calories of heat?A. 1.0 gram B. 2.0 grams C. 20 gramsD. 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 bythe addition of 4800 calories of energy?

A. 60 gramsB. 166 gramsC. 2.1 gramsD. 600 grams

# calories = mass x heat of fusion4800 calories = mass ice x 80 cal/ g Mass ice = 4800 calories / 80 cal/gMass = 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

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 hightemperature to a body at a lower temperature.

• Heat flows spontaneously from a body at a hightemperature to a body at a lower temperature.Heat is transferred when faster moving, hightemperature molecules collide with slower moving,lower temperature molecules. As a result of thecollision, the slower moving molecules speed up

and thus heat up.

FAHRENHEIT

• Temperatures are measured by thermometers.The first thermometer was created by GabrielFahrenheit (1686-1736). Fahrenheit noticed thatthe level of some mercury in a tube rose and fellaccording to how hot or cold it was in hislaboratory.

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 (1701-1744) studied Fahrenheit’swork and devised a thermometer using the boilingpoint and freezing point of water as his fixed

points.The freezing point and boiling points of water aremore reproducible than Fahrenheit’s bodytemperature 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 (1824-1907), known as LordKelvin, first suggested a temperature scale whichwas based on the Celsius scale but does not havenegative numbers. He achieved this by setting thelowest possible temperature as “0."

KELVIN

• The Kelvin scale uses the same fixed points, theboiling point and freezing point of water, and thesame divisions as the Celsius scale.

ABSOLUTE ZERO

• Lord Kelvin’s zero point became known as“Absolute Zero.” At absolute zero, all

molecularmotion ceases.

• Absolute zero is defined as the lowest possibletemperature and is believed to be -273.15°C.

STANDARD TEMPERATURE

• Standard temperature is defined as 0°C or 273 K.

• 0°C is chosen as standard temperature because itis easily obtained and maintained. The sampleneed only to immersed in a container of meltingice 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 + 273.

Convert 100°C to degrees Kelvin.

°K = 100°C + 273 = 373 K

PROBLEMS????

• Convert from 200 K to °C.• °C = 200 K - 273 = -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 theirrepeated collision with its sides. This force isdependent upon three factors; the mass of theparticles, the number of particles in the container,and their velocity which is related to theirtemperature.

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 abarometer. A barometer consists of a sealed glasstube filled with mercury and inverted into acontainer filled with mercury. The mercury in thetube will fall until the weight of the mercury in thetube 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 (1608-1647), the inventor of

• the mercury barometer.1 atm = 760 mm Hg = 14.7 lb/in21 atm = 760 torr = 101.325 kPa

MERCURY MANOMETER

• Another method of measuring pressure is with amercury manometer. Any change of pressure insidethe flask changes the level of the mercury in themanometer. 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?

WHAT IS THE PRESSURE INSIDE THE FLASK?

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