Foundations of Physics CPO Science Foundations of Physics Unit 8, Chapter 25

Unit 8: Matter and Energy Chapter 25 Energy, Matter, and Atoms 25.1 Matter and Atoms 25.2 Temperature and the Phases of Matter 25.3 Heat and Thermal Energy

Chapter 25 Objectives Describe the relationship between atoms and matter. Find an element in the periodic table. Identify the differences between elements, compounds, and mixtures. Convert temperatures between Fahrenheit, Celsius, and Kelvin scales. Understand the concept of absolute zero temperature. Describe the phases of matter and explain solid, liquid, and gas in terms of energy and atoms. Describe the concepts of heat and thermal energy and apply them to real-life systems. Perform basic calculations with specific heat.

Chapter 25 Vocabulary Terms atom compound element mixture molecule periodic table Kelvin Celsius thermometer Fahrenheit specific heat temperature calorie absolute zero random melting point heat of vaporization boiling point evaporation ionized condensation thermal energy relative humidity British thermal unit (BTU) heat solid plasma liquid heat of fusion gas

25.1 Matter and Atoms Key Question: What are the properties of different elements? *Students read Section 25.1 AFTER Investigation 25.1

25.1 Matter and Atoms We have partial answers to these three questions for all types of matter: What is the smallest piece of matter? Why can the same kind of matter assume different forms, like solid or liquid? How can one kind of matter (like wood) turn into another kind of matter with very different properties (like ashes)?

25.1 Brownian Motion A large floating dust speck moves smoothly because it is much larger than a particle of water. A tiny dust speck shows Brownian motion because of collisions with particles of water.

25.1 Size of atoms The head of a pin contains more than 1020 atoms. A sheet of thin aluminum foil is 200,000 atoms thick.

25.1 Classification of matter A molecule is a group of two or more atoms that are joined together. Most matter you encounter is made of molecules, or mixtures of molecules.

25.1 First theory of matter The ancient Greeks proposed that all matter was made of four fundamental elements: air, fire, water, and earth.

25.1 Elements Today we know that nearly all the matter in the world is made from 92 different elements. The periodic table shows the elements in order from atomic number 1 (hydrogen) to number 92 (uranium).

25.1 Elements At the time of this writing, scientists have created elements 93 to 116 in research laboratories. We don’t find much of elements 93 to 116 in nature because all of these elements are radioactive and break down into other elements.

25.2 Temperature and the Phases of Matter Key Question: What is temperature? *Students read Section 25.2 AFTER Investigation 25.2

25.2 Temperature and the Phases of Matter In the Fahrenheit scale, water freezes at 32 degrees and boils at 212 degrees The Celsius scale divides the difference between the freezing and boiling points of water into 100 degrees (instead of 180).

25.2 Converting temperatures A friend in Paris sends you a recipe for a cake. The French recipe says to bake the cake at a temperature of 200°C for 45 minutes. At what temperature should you set your oven, which reads temperature in Fahrenheit? 1) You are asked for the temperature in Fahrenheit. 2) You are given the temperature in Celsius. 3) Use the conversion formula TF = (9/5)TC + 32. 4) TF=(9/5)(200) + 32 = 392 degrees

25.2 Temperature and the Phases of Matter All thermometers are based on some physical property (such as color or volume) that changes with temperature. A thermistor is a device that changes its electrical resistance as the temperature changes. A thermocouple is another electrical sensor that measures temperature.

25.2 Temperature and the Phases of Matter Temperature measures the kinetic energy per atom due to random motion. Random motion is motion that is scattered equally in all directions. In pure random motion the average change in position is zero.

25.2 Temperature and the Phases of Matter When the temperature gets down to absolute zero, the atoms are said have the lowest energy they can have and the temperature cannot get any lower. Technically, we believe atoms never stop moving completely. Figuring out what happens when atoms are cooled to absolute zero is an area of active research.

25.2 Temperature and the Phases of Matter The Kelvin temperature scale is useful for many scientific calculations because it starts at absolute zero. The Kelvin scale is used because it measures the actual energy of atoms. A temperature in Celsius measures only the relative energy, relative to zero Celsius.

25.2 Phases of Matter The three most common phases of matter are called solid, liquid, and gas. At temperatures greater than 10,000 K the atoms in a gas start to break apart. In the plasma state, matter becomes ionized.

25.2 Phase changes When thermal energy is added or subtracted from a material, either the temperature changes, or the phase changes, but usually not both at the same time.

25.2 Change from solid to liquid The melting point is the temperature at which a material changes phase from solid to liquid. Melting occurs when the kinetic energy of individual atoms equals the attractive force between atoms. The heat of fusion is the amount of energy it takes to change one kilogram of material from solid to liquid or vice versa.

25.2 Energy and Heat of Fusion (J/kg) E = mhf Heat energy (J) Mass (kg)

25.2 Calculate Energy How many joules does it take to melt a 30 gram ice cube at 0°C? 1) You are asked for heat energy (E) in joules. 2) You are given mass (m) and that the material is ice. 3) Use the phase change equation E = mhf 4) E = (0.03 kg)(335,000 J/kg = 10,050 J

25.2 Evaporation Evaporation occurs when molecules go from liquid to gas at temperatures below the boiling point. Evaporation takes energy away from a liquid. The average energy of the molecules left behind is lowered. Evaporation cools the surface of a liquid because the fastest molecules escape and carry energy away.

25.2 Condensation Condensation occurs when molecules go from gas to liquid at temperatures below the boiling point. Condensation raises the temperature of a gas because atoms in a gas have more energy than atoms in a liquid. When air is saturated, it means the processes of evaporation and condensation are exactly balanced.

25.2 Change from liquid to gas The boiling point is the temperature at which the phase changes from liquid to gas. Just as with melting, it takes energy for an atom to go from liquid to gas. The heat of vaporization is the amount of energy it takes to convert one kilogram of liquid to one kilogram of gas.

25.2 Energy and Heat of Vaporization (J/kg) E = mhv Heat energy (J) Mass (kg)

25.2 Calculate Energy A steam iron is used to remove the wrinkles from clothes. The iron boils water in a small chamber and vents steam out the bottom. How much energy does it require to change one-half gram (0.0005 kg, or about half a teaspoon) of water into steam? 1) You are asked for the heat energy required (E) in joules. 2) You are given that the material is water, and the mass (m) is 0.0005 kg. 3) The heat of vaporization equation applies: E = mhv. 4) E = (0.0005 kg) (2,256,000 J/kg) = 1,128 joules. A typical steam iron takes about 5 seconds to boil this amount of water.

25.3 Heat and Thermal Energy Key Question: What is the relationship between heat, temperature, and energy? *Students read Section 25.3 AFTER Investigation 25.3

25.3 Heat and Thermal Energy Temperature is NOT the same as thermal energy. Thermal energy is energy stored in materials because of differences in temperature. The thermal energy of an object is the total amount of random kinetic energy for all the atoms in the object. Remember, temperature measures the random kinetic energy of each atom.

25.3 Heat and Thermal Energy Imagine heating a cup of coffee to a temperature of 100°C. Next think about heating up 1,000 cups of coffee to 100°C. The final temperature is the same in both cases but the amount of energy needed is very different. It takes more energy to heat up 1,000 cups than to heat up a single cup. The amount of thermal energy depends on the temperature and also on the amount of matter you have.

25.3 Heat and Thermal Energy Heat is what we call thermal energy that is moving. The joule (J) is the unit of heat (or thermal energy) used for physics and engineering. The calorie is a unit of heat often used in chemistry. Heat flows from the hot coffee to the cooler air in the room.

25.3 Specific Heat The specific heat is the quantity of heat it takes to raise the temperature of one kilogram of material by one degree Celsius.

25.3 Specific Heat The temperature of gold rises quickly compared with water because its specific heat is much less than the specific heat of water.

Specific heat (J/kgoC) 25.2 Heat Equation Specific heat (J/kgoC) Heat energy (J) E = mcp(T2-T1) Change in Temperature (oC) Mass (kg)

25.2 Calculate Heat One kilogram of water is heated in a microwave oven that delivers 500 watts of heat to the water. One watt is a flow of energy of one joule per second. If the water starts at 10°C, how much time does it take to heat up to 100°C? 1) You are asked for the time (t) to reach a given temperature (T2). 2) You are given the mass (m) of water, power (P), and initial temperature (T1). The specific heat of water is 4,184 j/kgoC. 3) The heat equation, E = mcp(T2-T1), gives the heat required. Power is energy over time: P = E/t. 4) First, calculate the heat required: E = (1 kg) (4,184 J/kgoC) (100oC - 10oC) = 376,560 joules. Next, recall that 500 watts is 500 joules per second. At 500 J/sec, it takes 376,560÷500 = 753 seconds, or about 12.6 minutes. NOTE: Specific heat often changes with temperature and pressure.

26.3 First Law of Thermodynamics Energy loss is equal to energy gain.

26.3 Second Law of Thermodynamics

Application: The Refrigerator