Heat, Temperature and the Zeroth Law of Thermodynamics PDF

Heat, Temperature and the Zeroth Law of Thermodynamics BEVERLY L. GARCIA Subject Teacher MELC Convert temperatures and temperature differences in the following scales: STEM_GP12TH-IIg-50 Fahrenheit, Celsius, Kelvin Define coefficient of thermal expansion and...

Heat, Temperature and the Zeroth Law of Thermodynamics BEVERLY L. GARCIA Subject Teacher MELC Convert temperatures and temperature differences in the following scales: STEM_GP12TH-IIg-50 Fahrenheit, Celsius, Kelvin Define coefficient of thermal expansion and coefficient of volume expansion STEM_GP12TH-IIg-51 Calculate volume or length changes of solids due STEM_GP12TH-IIg-52 to changes in temperature Solve problems involving temperature, thermal expansion, heat capacity, heat STEM_GP12TH-IIg-53 transfer, and thermal equilibrium in contexts such as, but not limited to, the design of bridges and train rails using steel, relative severity of steam burns and water burns, thermal insulation, sizes of stars, and surface temperatures of planets What is the difference between a hot cup of coffee and a cold cup of water? In a hot cup of coffee there is more activity – the atoms are jiggling around more. We say that they have more kinetic energy. We might even say that they have more thermal energy (energy of random motion) or more internal energy because more energy is internal to the system. Which has more internal energy, a cup of hot water or an iceberg? The iceberg because it has more molecules jiggling. The iceberg is having huge mass which accounts for its greater internal energy.  THERMAL PHYSICS Explores the internal energy of objects due to the motion of atoms and molecules comprising the objects Explores the transfer of this energy from object to object known as heat. Thermodynamics is the study of heat, energy transformation, work and temperature and the relation of heat to other forms of energy and properties of matte 5 Heat and Temperature The heat that flows from hot to cold originates in the internal energy of the hot substance. It is not correct to say that a substance contains heat. Internal energy (Thermal Energy) is the total energy that the molecules possess (kinetic plus potential). Kinetic energy can be translational and rotational. Molecules have potential energy because of intermolecular forces. When we heat a substance, we increase its internal energy. Temperature is related to the internal energy per molecule or the average kinetic energy of translational motion of molecules. Internal Energy of the System, U Internal energy, U, is the total kinetic energy and potential energy of all the molecules in the system. Kinetic energy refers to the energy associated with the motion of the particles making up the system Potential energy— refers to the energy associated with the static components of matter like chemical bonds Average Kinetic Energy and Temperature 7.4x10-21 J 9 Heat and Temperature Heat and temperature are two related but different quantities. Temperature is defined as a measure of the average kinetic of molecules making up an object Heat is energy in transit from one body to another due to a difference in temperature. TEMPERATURE In everyday language, temperature is a measure of how hot or cold an object is. On the molecular level, temperature is defined as a measure of kinetic energy of molecules making up an object. The instrument used to measure temperature is thermometer. Temperature, just like any other physical quantity, requires a standard measurement. These standards are the three common scales which are the Fahrenheit, Celsius and Kelvin. 1. Celsius temperature scale – it is the common scale use to measure temperature. In this temperature scale, the 0º C` is the freezing point and 100ºC is the boiling point. 2. Fahrenheit Scale - This scale sets the temperature of the ice point at 32°F and the temperature of the steam point at 212°F. 3. Kelvin Scale – This is the most used absolute temperature scale in the world. Since it is an absolute scale, temperatures express in Kelvin are not measured in degrees. Temperature Conversions To convert Celsius to Fahrenheit: 𝟗 𝑻𝑭 = 𝑻𝑪 + 𝟑𝟐° 𝟓 To convert Fahrenheit to Celsius: 𝟓 𝑻𝑪 = (𝑻𝑭 − 𝟑𝟐°) 𝟗 To convert Celsius to Kelvin: 𝑻𝑲 = °𝑪 + 𝟐𝟕𝟑. 𝟏𝟓 where: 𝑻𝑭 = 𝑻𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆 𝒊𝒏 𝑭𝒂𝒉𝒓𝒆𝒏𝒉𝒆𝒊𝒕 𝑻𝑪 = 𝑻𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆 𝒊𝒏 𝑪𝒆𝒍𝒔𝒊𝒖𝒔 𝑻𝑲 = 𝑻𝒆𝒎𝒑𝒆𝒓𝒂𝒕𝒖𝒓𝒆 𝒊𝒏 𝑲𝒆𝒍𝒗𝒊𝒏 Example: Temperature Conversions Convert 50ºC into ºF Convert 40ºC into ºC To convert Celsius to Fahrenheit: 𝟗 𝑻𝑭 = 𝑻𝑪 + 𝟑𝟐° 𝟓 To convert Fahrenheit to Celsius: 𝟓 𝑻𝑪 = (𝑻𝑭 − 𝟑𝟐°) 𝟗 To convert Celsius to Kelvin: 𝑻𝑲 = °𝑪 + 𝟐𝟕𝟑. 𝟏𝟓 38.6 oC, 311.75 K 14 HEAT Heat is the transfer of thermal energy from a higher- temperature object to a lower-temperature object because of a difference in temperatures. This is typically accomplished through particle interactions (collisions) in which momentum is transferred from one object to another. SI Unit of Heat: joule (J) or calories (cal) Symbol: Q 4.184 J = 1 cal 4184 J = 1 kcal Heat Capacity and Specific Heat The heat capacity C of a particular sample is defined as the amount of energy needed to raise the temperature of that sample by 1°C. From this definition, we see that if energy Q produces a change ∆T in the temperature 𝑸 of a sample, then 𝑸 = 𝑪 ∆𝑻 𝑪= ∆𝑻 The specific heat, c of a substance is the heat capacity per unit mass. Therefore, if energy Q transfers to a sample of a substance with mass m and the temperature of the sample changes by ∆T, the specific heat of the substance is 𝑸 𝑸 = 𝒎𝒄∆𝑻 𝒄= 𝒎 ∆𝑻 where Q = heat m= mass of the substance ∆T=temperature change C = heat capacity c = specific heat capacity Example How much heat is needed to raise the temperature of a 3 kg of aluminum to 8 ℃? Step 1: Given: m = 3𝑘𝑔; 𝑐𝐴𝑙 = 900 𝐽/𝑘𝑔 ∙ ℃ ; ∆𝑇 = 8 ℃ Step 2: Equation: 𝑄 = 𝑚𝑐 ∆𝑇 Step 3: Solution: 𝑄 = 3𝑘𝑔 900 𝐽Τ𝑘𝑔 ∙ ℃ 8℃ 𝑄 = 21 600 𝐽 17 Heat Transfer CLOSED SYSTEM - a system that prevents its components from exchanging energy (such as heat ) with the surroundings Heat Transfer  THERMAL EQUILIBRIUM and the ZEROTH LAW OF THERMODYNAMICS If two objects at different temperatures are placed in a thermal contact, they eventually come to the same temperature or they are then said to be in thermal equilibrium. This concept was used by a British physicist and astronomer named Ralph H. Fowler in 1931 20  THERMAL EQUILIBRIUM and the ZEROTH LAW OF THERMODYNAMICS The Zeroth Law of Thermodynamics states that “if two systems or objects are in thermal equilibrium with a third system or object, then they are in thermal equilibrium with each other”. For example, if object A is in thermal equilibrium with object B, and object A is in thermal equilibrium with object C, then object B must be in thermal equilibrium with object C. 21 Methods of Heat Transfer Conduction: Convection: Radiation: the transfer of energy in the transfer of energy as a the transfer of energy bodies that are in contact result of energetic (heated) through electromagnetic with each other. This is particles moving from one waves. due to the collision of place to another. molecules of the bodies in contact Heat: Phase Change Example 24 Heat: Phase Change Phase - described as solid, liquid or gas Phase change — transition from one phase to another due to addition or removal of heat. Solid to liquid - melting (opposite direction: freezing) Liquid to gas - vaporization (opposite direction: condensation) Solid to gas - sublimation During phase change there is no change in temperature. Q= 𝑚𝐶ΔT cannot be used to determine the amount of heat involved during phase change Heat: Phase Change Latent Heat — the amount of heat needed for 1 g of an object to undergo phase change. Symbol: L 𝑸 𝑳= 𝒎 Sl unit: J/g Other unit: cal/g Latent heat depends on the material and type of phase transition; each material has a unique latent heat for each type of phase transition. L is negative if heat is released during phase change L is positive if heat is absorbed during phase change Heat: Phase Change Phase - described as solid, liquid or gas Phase change — transition from one phase to another due to addition or removal of heat. Solid to liquid - melting (opposite direction: freezing) Liquid to gas - vaporization (opposite direction: condensation) Solid to gas - sublimation During phase change there is no change in temperature. Q= 𝑚𝐶ΔT cannot be used to determine the amount of heat involved during phase change Example: Latent Heat of Fusion 28 Example: Latent Heat of Fusion 29 Example: Latent Heat of Fusion 30  Why railroad rails are laid with gaps between them? Thermal Expansion When we stack drinking glasses one inside the other in the cupboard, both of them may stick together and one or both of them may break when twisted apart. What is the safe way of separating them? Thermal Expansion LINEAR EXPANSION – one dimensional The change in length Δ𝐿 is directly proportional to the change in temperature Δ𝑇 and original length of the object, 𝐿0. Δ𝐿= 𝛼 𝐿0 Δ𝑇 Where: Δ𝐿 = change in length, meter (m) 𝐿0= original length, meter (m) Δ𝑇= temperature change, degree Celsius (𝐶°) 𝛼 = coefficient of linear expansion, 𝐶°-1 The change in length may be negative means a decrease in length (contraction) or positive means an increase in length (expansion) depending on the change in temperature. The coefficient of linear expansion (𝛼) describes how the length of a particular object changes with change in temperature. Example: A steel beam is used in the construction of bridge is 9.5 m long at 23℃. On a hot summer day, the temperature increases to 42℃. What is the change in length due to linear expansion? 34 VOLUME EXPANSION – one dimensional The change in volume of a material which undergoes a temperature change is given by a relation similar to linear expansion, namely: Δ𝑉= 𝛽 𝑉0 Δ𝑇 Where: Δ𝑉 = change in volume, liter (L) 𝑉0= original volume, liter (L) Δ𝑇= temperature change, degree Celsius (𝐶°) 𝛽 = coefficient of volume expansion, 𝐶°−1 The amount a material expands is characterized by the material’s coefficient of expansion The coefficient of volume expansion (𝛽) is normally equal to approximately three times the coefficient. The coefficient of volume expansion for liquid is greater than that of solids. Relationship of the Coefficients of Thermal Expansion  Coefficient of Linear & Volume Expansion of Common Materials 20XX presentation title 37 Example: A gasoline tank in a car has a capacity of 65 L at 20℃. If the tank is fully filled without a cover, how much gasoline will overflow if the car is left in the sun and the gasoline reaches a temperature of 40℃? 38 Seatwork: 39 thank you