Chapter 10 H E A T
Ch 10-1: Temperature andThermal Equilibrium • Determining an object’s temperature with precision requires • a definition of temperature • established measurements that determine how “hot” or “cold” objects are
Heat Energy • Energy must be added to or removed from a substance to change its temperature. • Temperature is PROPORTIONAL to the kinetic energy of atoms.
Thermal Energy… • Internal Energy – the energy of a substance due to the random motions of its component particles and equal to the total energy of those particles.
Internal Energy • For an ideal gas, the internal energy depends only on the temperature of the gas. • For gases with 2 or more atoms per molecule, as well as for liquids and solids, other properties besides temperature contribute to the internal energy.
INTERNAL ENERGY • The symbol, U, stands for internal energy • Thus, delta U, stands for the change in internal energy
Heating and Cooling • If an object has become hotter, it means that it has gainedheat energy. • If an object cools down, it means it has lostenergy
Thermal Equilibrium • The state in which two bodies in physical contact with each other have identical temperatures
Thermal Equilibrium • Ex: When you put a warm coke can into a large beaker of cold water, there is a noticeable temperature difference between the two. • After about 15 minutes, the can of soda will be cooler and the water surrounding it will be slightly warmer. Eventually, both the can and the water will be at the same temperature. • This temperature will not change as long as conditions remain unchanged in the beaker. This is Thermal Equilibrium.
Thermal Equilibrium is the basis for measuring temperature with thermometers. • This is because the thermometer is at the same temperature, or is in thermal equilibrium with, the object.
HEAT ENERGY What is HEAT? Form of energy and measured in JOULES Particles move about more and take up more room if heated – this is why things expand if heated It is also why substances change from: solids liquids gases when heated
Matter and Temperature • Matter Expands as its temperature increases • This is known as Thermal Expansion
Heating and Cooling cont… • Heat energy always moves from:HOTobject COOLER object e.g. Cup of water at 20 °C in a room at 30°C - gains heat energy and heats up – its temperature rises Cup of water at 20 °C in a room at 10°C loses heat energy and cools down – its temperature will fall.
Measuring Temperature • Units depend on scale used: • Fahrenheit, Celsius, and Kelvin (or absolute) scales. • Fahrenheit commonly used in US • Fahrenheit and Celsius temps can be converted…
The Fahrenheittemperature scale is an English measurement scale. FREEZING POINT:Water freezes at 32 oF and BOILING POINT:boils at 2l2 oF.The Fahrenheit degree is smaller than theCelsius degreeorKelvin.
On the Celsius temperature scale, (the METRIC SCALEbased on the freezing and boiling point of water) water’sfreezing point is 0 oC& water’s boiling point is l00 oC
The Kelvin (K) scale is based on the boiling and freezing point of water and absolute zero.The Kelvin scale does not use the degree symbol. The units are Kelvins (K), not degrees Kelvin. 1 Kelvin unit = 1 oC scale.
On this scale the lowest possible temperature is absolute zero, written ”0 K." At absolute zero, the average kinetic energy of particles is zero.Absolute zero on the Kelvin scale is equal to -273 degrees Celsius.
Temperature Conversion Formulas:oC = K – 273K = oC + 273oC = (oF-32) 1.8oF = (1.8oC) + 32
HOMEWORK:Page 363: #1-3 allTHIS WILL BE FOR A GRADE WHEN YOU WALK INTO CLASS TOMORROW!!!Must show all work
QOTD • What is the boiling point of water in degrees Fahrenheit? • What is the freezing point of water in degrees Celsius? • What is the value of absolute zero?
QOTD • What is the boiling point of water in degrees Fahrenheit? • 212 degrees • What is the freezing point of water in degrees Celsius? • 0 degrees • What is the value of absolute zero? • 0 Kelvin
10-1 Review Questions • Which of the following is true for the water molecules inside popcorn kernels during popping? A: Their Temperature Increases. B: They are destroyed. C: Their Kinetic Energy Increases. D: Their mass changes.
HEAT and ENERGY • HEAT: the energy transfer between two objects because of a difference in their temperatures. • Energy transferred as heat ALWAYS transfers from an object of a higher temp to that of a lower temp.
Internal Energy • If the can and the water in the glass reach thermal equilibrium, which has greater internal energy?
Internal Energy • If the can and the water in the glass reach thermal equilibrium, which has greater internal energy? • A: The glass of water because of its greater mass
Thermal energy is unique in that it does NOT exist by itself. Thermal energy is present ONLY when another form of energy is present.
Thermal energy is unique in that it does NOT exist by itself. Thermal energy is present ONLY when another form of energy is present.Ex.Thermal energy like body heat only exist from breaking chemical bonds in food.Ex.Heatfrom the motion offrictionEx. Electrical items get hot from something resisting the flow of electricity. …….Etc.
Key Points to remember… • Temperature – measures the average KE of molecules in an object • HEAT – energy transferred from one object to another • Internal Energy – sum of the energies of the molecules.
The calorie – the quantity of heat needed to raise the temperature of one gram of water10C.1 calorie = 4.18 joules
The calorie – The Calorie (also called a kilocalorie) – often measures the energy content in food 1 Calorie= 1000 caloriesThere is a difference!
1 Calorie = 1000 caloriesThere is a difference!Example item: That means a 190 Calorie bowl of cereal REALLY has 190,000 caloriesof energy!
Heat - units of Energy • Heat Energy (heatflow): Q • Internal energy: U calorie (cal) = 4.186 J kilocalorie (kcal) = 4186 J Calorie (dietary Calorie) = 1 kcal = 4186 J Thus, for every Calorie you consume you actually obtain 4186 J of energy
Heat and Work • Friction can increase a substances internal energy • For solids, internal energy can be increased by deforming their structure. • EX: Rubber band stretched or a piece of metal bent.
Rubber Band Activity… • Purpose: To demonstrate how work increases an object’s internal energy. • Procedure: Hold the rubber band between your thumbs. Touch the middle section of the rubber band to your lip and note how it feels. Rapidly stretch the rubber band and keep it stretched. Touch the middle section of the rubber band to your lip again. Notice is the rubber band’s temperature has changed. (you may have to repeat this procedure several times before you can clearly distinguish the temperature difference.)
Conservation of Energy • If changes in internal energy are taken into account along with changes in mechanical energy, the total energy is a universally conserved property PE + KE + U = 0
Ex: Conservation of Energy • A 0.10 kg ball falls 10 m onto a hard floor and then bounces back up 9.0 m. How much of its mechanical energy is transformed to the internal energy of the ball and the floor? ball
Ex: Conservation of Energy A 0.10 kg ball falls 10 m onto a hard floor and then bounces back up 9.0 m. How much of its mechanical energy is transformed to the internal energy of the ball and the floor? Givens: m = 0.10 kg g = 9.81 U = ? h = 10.0 m PE = ? KE=? Formula: PE + KE + U = 0 Or PEi + KEi + Ui = PEf + KEf + Uf
Ex: Conservation of Energy A 0.10 kg ball falls 10 m onto a hard floor and then bounces back up 9.0 m. How much of its mechanical energy is transformed to the internal energy of the ball and the floor? Givens: m = 0.10 kg g = 9.81 U = ? h = 10.0 m PE = ? KE= ? Formula: Delta PE + Delta KE + Delta U = 0 or PEi + KEi + Ui = PEf + KEf + Uf mg( h) + 0 + Uf-Ui = 0 mg ( h) = U 0.10 (9.81) (1) = U 0.98 J
HOMEWORK • Page 370 Practice: # 1 • Page 370 Review: # 1 and 3
QOTD 1: A substance’s temperature increases as a direct result of: a. Energy being removed from the particles of the substance b. Kinetic Energy being added to the particles of the substance c: A change in the number of atoms and molecules in a substance
QOTD CONT 2: What happens to the internal energy of an ideal gas when it is heated from 0 degrees Celsius to 4 degrees Celsius? a: increases b: decreases c: stays the same d: impossible to determine
QOTD cont • Which of the following is proportional to the KE of atoms and molecules? a: Elastic Energy b: Thermal Equilibrium c: Potential Energy d: Temperature
QOTD • Heat Flow occurs between two bodies in thermal contact when they differ in which of the following properties? A: mass B: density C: temperature D: specific heat
QOTD • Which of the following is equivalent to 88 degrees Fahrenheit? A: 49 degrees C B: 31 degrees C C: 16 degrees C D: 58 degrees C
10-3: Changes in temperature and phase • Specific Heat Capacity: the quantity of energy needed to raise the temperature of 1 kg of substance by 1 degree Celsius at constant pressure.
Specific Heat Capacity (c) • Relates mass, temperature change, and energy transferred as heat. • Specific heat capacity equation: cp = Q/m(T) Where the subscript p represents heat capacity measured at a constant pressure
Specific Heat • Though heat and temperature are not the same thing, there is a correlation between the two, captured in a quantity called specific heat, c. • Specific heat measures how much heat is required to raise the temperature of a certain mass of a given substance.
See page 372 • Table 10-4 Specific Heat capacities • **You must know cp for water = 4.186 x 103 J/(kg * C)