Energy There are many forms of energy: solar, electrical, nuclear, mechanical...... but only two types: Potential energy = energy due to position, condition, or composition. a compressed spring chemical bonds in gasoline, coal, or food Gravitational potential energy (due to mass and height) Kinetic Energy = energy due to movement. Bullet Water flowing over a dam Steam The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed.

Heat = transfer of thermal energy The Kinetic energy associated with the random motion of molecules is called Thermal energy. The amount of thermal energy in an object is given by its temperature. time Hot coffee Temperature is high Higher thermal energy Cold coffee Temperature is low Lower thermal energy The change in temperature is due to a transfer of thermal energy from the coffee (system) to its surroundings (room). Heat = transfer of thermal energy from one system to another due to a temperature difference. energy in transit

Temperature = a quantitative description of hotness or coldness To use temperature as a measure of hotness or coldness, we need to construct a temperature scale. This is what we call a thermometer. To convert from one T scale to another: 1.8, 32 and 273 are defined numbers and therefore are exact numbers

Example -- Solving a Temperature Problem A person with hypothermia has a body temperature of 34.8 °C. What is that temperature in °F? TF = 1.8 (TC) + 32 ° TF = (1.8) (34.8 °C) + 32 ° exact 3 sf = 62.6 ° + 32 ° 1 decimal pl. exact = 94.6 °F 1 decimal pl. 4

the amount of heat required to raise the T of 1g of water by 1 ˚C At the beginning, scientist started to measure heat in terms of its ability to raise the T of water. the amount of heat required to raise the T of 1g of water by 1 ˚C calorie In 1948, scientists decided that since heat (like work) is transferred energy, the SI unit of heat (the joule) should be the one to use for energy. In honor of 19th century English physicist Prescott Joule Symbol is capital J Pronounced “jewel” Energy Units joule The calorie is now defined to be 4.184 J, with no reference to the heating of water. 1 cal = 4.184 J (exactly) The “calorie” used in nutrition, sometimes called the Calorie (Cal), is really a kilocalorie. 1 Cal = 1 kcal = 1000 cal.

2.1 Practice 1. When 1.0 g of octane fuel burns in an automobile engine, 48 000 J are released. Convert this quantity of energy to calories: 2. In a type of cancer treatment called thermotherapy, temperatures as high as 113 ˚F are used to destroy cancer cells. What is that temperature in degrees Celsius? 3. State the temperature (˚C), including the estimated digit. 6

The amount of heat transferred, depends on 3 factors: It takes twice the amount of heat to boil 2 cups of water than 1 cup The amount of substance: 10 g 1000g It take more heat to raise the T by 100 degrees than by 10 degrees The T change of the substance: ∆T = 0.001 ˚C ∆T = 1000000 ˚C = Tf-Ti The nature of the substance Ability of a specific material to incorporate (absorb) heat The specific heat : Water Gold

Practice---using the heat equation A hot-water bottle contains 750 g of water at 65 °C. If the water cools to body temperature (37 °C), how many calories of heat could be transferred to sore muscles? STEP 1 Given: Want: 750 g of water ? heat cools from 65 °C to 37 °C Conversion factor or equation STEP 2 plan: Heat = mass x Δ T x SH STEP 3 execute: the temperature change ΔT 65 °C – 37 °C = 28 °C 750 g x 28 °C x 1.00 cal = 21 000 cal g °C

Food = Energy Potential Energy Nutritional calorie (Cal) = 1 kcal = 1000 cal 2000 Cal = 2000 kcal = 2,000,000 calories 2 million cal Chapter 2, Unnumbered Figure, Page 76 The FDA recommends 30% of total intake from fat calories. For a female adult the level is around 2,000 calories per day, with 600 fat calories. For a male adult the level is around 2,500 calories per day, with 750 fat calories.

Practice 4. How many kilojoules are needed to raise the temperature of 325 g of water from 15.0 °C to 77.0 °C? 1) 20.2 kJ 2) 84.3 kJ 3) 105 kJ 5. At a fast-food restaurant, a hamburger contains 37 g of carbohydrate, 19 g of fat, and 24 g of protein. What is the energy content for each food type and the total energy content, in kcal? 6. Use table 3.10 to determine the number of hours of running needed to burn off the calories in this meal. 10

Classification of Matter Figure 02-T07 Title: Classification of Matter Caption: 11

More movement of particles Gas High E Lots of movement Three States of Water Solid Low E state No movement Rigid structure Liquid Intermediate E More movement of particles Gas High E Lots of movement Particles are free from one another Physical change Physical change Figure 02-CI3B Title: States of Matter Caption: Answer the following questions for the water samples A and B shown in the diagrams: a. Which sample has its own shape? b. When each sample is transferred to another container, what happens to its volume? c. Match the diagrams (1, 2, or 3) that represent the water particles with sample A and B. Give a reason for your choice. Physical change  the identity and composition of the substance does not change. The amount of heat per unit mass that must be transferred for a sample to completely undergo a phase change is called heat of transformation, ΔH. ΔH = q q = heat m 12

Melting = change from the solid state to liquid state. Heat is required to free particles from their rigid structure. heat needed to melt a solid the amount of heat The heat of fusion= ΔHf For water: 334 J or 80. cal 1 g of water heat released when liquid freezes

vaporizing = change from the liquid state to vapor (gas) state. Heat is required to free particles from one another. absorbed to vaporize 1 g of a liquid to gas at the boiling point Normal Boiling Point of Water = 100 °C The heat of vaporization = ΔHv For water: = 2260 J or 540 cal 1 g of water released when 1 g of a gas condenses to liquid at the boiling point

illustrates the changes of state as a solid is heated Figure 02-13 Title: Heating Curve Caption: (a) A heating curve diagrams the temperature increases and changes in state as heat is added. (b) A cooling curve for water. A heating curve illustrates the changes of state as a solid is heated uses sloped lines to show an increase in temperature uses plateaus (horizontal lines) to indicate a change of state A cooling curve illustrates the changes of state as a gas is cooled uses sloped lines to indicate a decrease in temperature uses plateaus (horizontal lines) to indicate a change of state 15

To calculate the heat involved in a plateau  q = m ΔH To calculate the heat involved in a slope  q = m x ΔT x SH ΔH v = heat of vaporization =540 cal/g 100 ˚C water ΔH f = heat of fusion = 80. cal/g 0 ˚ C Heat added  To calculate the heat involved in a plateau  q = m ΔH

Using the graph, determine the following: Practice Using the graph, determine the following: 7. A plateau (horizontal line) on a heating curve represents 1) a temperature change 2) a constant temperature 3) a change of state 8. How many plateaus are there on the graph? 9. A sloped line on a heating curve represents 10. How many sloped lines are there on the graph? Figure 02-13-15UN Title: Heating Curve Problem Caption: The following is a heating curve for chloroform, a solvent for fats, oils, and waxes. 11. The physical state of the substance present in the sloped lines. 12. The physical change taking place in the plateaus. 17

13. Use the graph to assign a beaker number to a letter on the graph Practice 13. Use the graph to assign a beaker number to a letter on the graph 14. Using the values for the heat of fusion, specific heat of water, or heat of vaporization, calculate the amount of heat needed to warm 20.0 g of water at 15 ˚C to 72 ˚C Figure 02-13-16UN Title: Heating Curve Problem Caption: Associate the diagrams shown with a segment on the heating curve for water. 18

Practice 15. A sports trainer applies an ice bag to the back of an injured athlete. Calculate the heat, in kilocalories, that is absorbed if 155 g of ice at 0.0 ˚C is placed in an ice bag, melts, and rises to body temperature of 37.0 ˚C.