Chapter 7 Notes. Matter is made of tiny particles in constant motion

Transcription

1 Chapter 7 Notes Section 7.1 Matter is made of tiny particles in constant motion Atomic Theory Greek philosophers (430 BC ) Democritus and Leucippus proposed that matter is made of tiny particles called atoms. For 2,300 years atoms were an idea that few believed. In 1803, John Dalton revived the idea of atoms, but lacked proof. Brownian motion In 1827, Robert Brown, a Scottish botanist, saw that the grains of pollen in water moved in an irregular, jerky way. After observing the same motion, he concluded that all tiny particles move in the same way. Evidence for atoms In 1905, Albert Einstein proposed that Brownian motion is caused by collisions between visible particles like pollen grains, and smaller, invisible particles. This was strong evidence that matter was indeed made of atoms. Historical Facts Ancient Chinese ideas A collection of ancient texts compiled by Confucius ( BC) discusses the basic building blocks of matter (metal, wood, water, fire, and earth). Some of the writings in these texts were already 1000 years old when Confucius collected and preserved them in five volumes known as The Five Classics. Ancient Indian ideas In India, writings from the 6 th century BC describe five elements earth, water, fire, air, and ether that make up the universe. The writings explain that all objects such as stones, gold, silver, and trees, are made up of the five elements. Ancient Greek ideas The Greek philosopher Empedocles of Acragas ( BC) explained that everything we see is made up of four basic elements: fire, water, air, and earth. Aristotle, another Greek philosopher, believed that Empedocles explanation was the best way to understand why there are so many different types of matter. Definitions: An element is defined An atom An molecule An compound An mixture

2 Section 7.2 Measuring temperature You are really measuring the amount of energy that a particular matter has at that particular time. Thermometer: an instrument that measures temperature (amount of energy). The uses the expansion of colored liquid. As the temperature increases, it expands and rises up a long, thin tube. All thermometers are based on a physical property (such as color or volume) that changes with temperature. A uses a thermistor to measure temperature. A in which chemicals that change color at different temperatures. (Eg. aquarium sticker thermometers - outside of the tank) Temperature Scales: Water F. P. B. P. Celsius: 0 C 100 C -273 absolute zero Fahrenheit: Kelvin: 273 K 373 K 0 K absolute zero Conversions between scales Fahrenheit to Celsius Celsius to Kelvin T c = T k = Celsius to Fahrenheit Kelvin to Celsius T f = T c =

3 TEMPERATURE CONVERSIONS Convert The Following Temperatures into Celsius Degrees: 1) 45 o F 2) 145 o F 3) 22 o F 4) - 95 o F 5) - 45 o F Convert The Following Temperatures into Fahrenheit Degrees: 6) 45 o C 7) 135 o C 8) 5 o C 9) - 10 o C 10) - 45 o C NOW CONVERT ALL OF THE ABOVE INTO KELVIN UNITS More Temperature Conversion Practice: C = K = F K = C = F F = C = K 4. 0 F = C = K 5. 0 C = F = K F = C = K

4 Temperature and energy Temperature is a measure of the kinetic energy of individual atoms. Imagine you had a microscope powerful enough to see individual atoms in a solid at room temperature. You would see that the atoms are in constant motion. The atoms in a solid material act like they are connected by springs (Figure 7.9). Each atom is free to move a small amount. When the temperature goes up, the energy of motion increases and the atoms jiggle around more vigorously. Average motion If you throw a rock, the rock gets more kinetic energy, but the temperature of the rock does not go up. How can temperature measure kinetic energy then? We already know the relationship between motion and kinetic energy for a single object (or atom). For a collection of atoms, the situation is different. The kinetic energy of a collection has two parts. The kinetic energy you know comes from the average motion of the whole collection, like the motion of the whole rock. The kinetic energy that comes from the average motion of all the atoms together is not what temperature measures. Random motion Each atom in the rock is also jiggling back and forth independently of the other atoms in the rock. This jiggling motion is random. Random motion is motion that is scattered equally in all directions. On average, there are as many atoms moving one way as there are moving the opposite way. Temperature and random motion Each atom in the rock has kinetic energy from its random motion, as well as from the average motion of the whole rock. Temperature measures the kinetic energy in just the random motion. Temperature is not affected by any kinetic energy associated with average motion. That is why throwing a rock does not make it hotter (Figure 7.10). When you heat a rock with a torch, each atom jiggles back and forth with more energy but the whole rock stays in the same place. Melting and boiling The higher the temperature, the higher the random kinetic energy of each atom. Hot atoms move faster than cold atoms. If you heat a rock with a torch long enough, the atoms get so much energy they start to break away from each other. The rock melts. If you keep heating even more the liquid rock will start to boil. In boiling some atoms have so much energy they leave the rock altogether and fly off into the atmosphere.

5 The phases of matter Solid, liquid, and gas A holds its shape and does not flow. The molecules vibrate in place, but on average, don t move far from their places. A holds its volume, but does not hold its shape it flows. The molecules are about as close together as they are in a solid, but have enough energy to exchange positions with their neighbors. flow because the molecules can move around. A flows like a liquid, but can also expand or contract to fill a container. A does not hold its volume. The molecules have enough energy to completely break away from each other and are much farther apart than molecules in a liquid or solid. Intermolecular forces These intermolecular forces have different strengths for different molecules. The strength of the intermolecular forces determines whether matter exists as a solid, liquid, or gas at any given temperature. Phase Changes = the change of a substance from one state to another at temperature and pressure Phase changes involve potential energy between particles. Heat of Fusion =(H f ) Heat of Vaporization = (H v ) Q = Q = Heat to Melt (or ) (Solid Liquid) Heat to Vaporize (or ) (Liquid Gas)

6 Section 7.3 What is Heat? is the sum of all of the kinetic energy of atoms or molecules added up together. Thermal energy depends on and. Two pots of water which are both heated to 85 o Celcius. #1 has 1,000 grams of water #2 has 2,000 grams of water. Which takes more energy? Why? What is heat? It is the flow of. Heat is really is thermal energy. (If there is a difference in the temperatures) *Heat always flows from the (higher energy) to the (lower energy). *********** Units of heat and thermal energy The joule is the metric unit for measuring heat. - The average hair dryer puts out 1,200 joules of heat every second! The calorie is defined as the quantity of heat needed to increase the temperature of of water by. - The unit used for measuring energy content of the food we eat is the kilocalorie, which equals 1,000 calories. The British Thermal Unit is defined as the quantity of heat it takes to increase the temperature of of water by. -The Btu is often used to measure the heat produced by heating systems or heat removed by air-conditioning systems. Specific Heat The specific heat is the amount of energy that will raise the temperature of one kilogram of material by one degree Celsius. You need to add of heat to 1 kg of water to raise the temperature by 1 C. You only need to raise the temperature of 1 kg of steel by 1 C. It takes 9 times more energy to raise the temperature of water by 1 C than it does to raise the temperature of the same mass of steel by 1 C. APPLE PIE!!! ****** Knowing the specific heat tells you how quickly the temperature of a material will change as it gains or loses energy.

7 Why is specific heat different for different materials? - Materials made up of heavy atoms or molecules have compared with materials made up of lighter ones. - This is because temperature measures the. - Heavy particles mean fewer molecules per kilogram. Energy that is divided between fewer particles means more energy per particle, and therefore more temperature change. Calculating energy changes from heat Q = m c (T 2 T 1 ) 1. How much heat is needed to raise the temperature of a 250-liter hot tub from 20 C to 40 C? The specific heat of water is 4,184 J/kg C. (HINT: 1 liter of water has a mass of 1 kilogram.) 2. How much heat energy is needed to raise the temperature of 2.0 kilograms of concrete from 10 C to 30 C? The specific heat of concrete is 880 J/kg C. 3. How much heat energy is needed to raise the temperature of 5.0 grams of gold from 20 C to 200 C? The specific heat of gold is 129 J/kg C.

8 7.4 Heat Transfer Heat conduction Conduction occurs between two materials at different temperatures and when they are each other. Eg. Holding a Hot cup of coffee. Convection Convection is the transfer of heat through the motion of fluids such as and. Thermal radiation is electromagnetic waves (including light) produced by objects because of their temperature. All objects with a temperature above absolute zero (-273 C or -459 F) emit thermal radiation. Thermal radiation comes from atoms Thermal radiation comes from the thermal energy of atoms. The power in thermal radiation increases with higher temperatures because the thermal energy of atoms increases with temperature (Figure 7.20). Because the sun is extremely hot, its atoms emit lots of thermal radiation. Objects emit and absorb radiation The temperature of an object if more radiation is absorbed. The temperature if more radiation is given off. The temperature adjusts until there is a between radiation absorbed and radiation emitted. ( ) The amount of thermal radiation absorbed depends on the surface of a material. Black surfaces Mirrored surfaces Thermal radiation can travel through the vacuum of space. Conduction and Convection cannot carry heat through space because both processes require matter to transfer heat. Thermal radiation also travels fast (EM Waves) - at the speed of light.

9 Thermal Equilibrium = As collisions continue, the molecules of the hotter material lose energy and the molecules of the cooler material gain energy. The kinetic energy of the hotter material is transferred, one collision at a time, to the cooler material. Eventually, both materials are at the same temperature. When this happens, they are in. Thermal equilibrium occurs when two bodies have the. No heat flows in thermal equilibrium because the temperatures are the same. Heat: (Q) Unit: Calories (cal) or Joules (J) Thermal Equilibrium Q lost = Q gained * Heat lost by the hot object = heat gained by the cold object Q = m c (T 2 T 1 ) Thermal Equilibrium Practice: kg of hot water at 90 o C is poured into 0.5 kg of cold water at 10 o C. a. How much heat does the hot water contain? b. How much heat does the cold water contain? c. What is the Total Energy of the mixture? d. What is the new temperature of the combined liquid?

10 2. Exactly 0.2 kg of hot water at 80 o C is poured into 0.1 kg of cold water at 20 o C. a. How much heat does the hot water contain? b. How much heat does the cold water contain? c. What is the Total Energy of the mixture? d. What is the new temperature of the combined liquid? 3. Exactly 1.2 kg of hot water at 95 o Celcius are poured into 0.8 kg of cold water at 15 o Celcius. a. How much heat does the hot water contain? b. How much heat does the cold water contain? c. What is the Total Energy of the mixture? d. What is the new temperature of the combined liquid?

11 The rate of heat transfer In nature, heat transfer always occurs from hot to cold until thermal equilibrium is reached. The rate of heat transfer is proportional to the difference in temperature. If the temperature difference is large, heat flows faster than when the temperature difference is small. Thermodynamics- the study of. 1st Law of Thermodynamics the total increase in thermal energy of a system is the sum of the work done on it and the heat added to it. 2nd Law of Thermodynamics - no machine can be made that only absorbs energy by heat and then entirely transfers the energy out of the engine by an equal amount of work. 3 rd law of Thermodynamics- Entropy - a measure of a systems disorder Systems with maximum disorder are favored. Increasing disorder reduces the energy available for work. The entropy of the universe increases in all natural processes. Entropy can increase or decrease within a system.