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Chemistry 30 Thermochemistry Notes A1. Energy ____________________: the study of energy transfer and energy changes ___________________ and ___________________ are a major store of chemical energy that we use in everyday lives. the energy stored in the chemical bonds of hydrocarbons originally comes from the ___________ ancient plants captured the energy of the sun during _______________________, ancient animals ate the plants, then death and trapping in rock formations as oil, gas, oil sand etc. the First Law of Thermodynamics states that: o the total energy of the universe is ____________________ o Energy is neither created nor destroyed, but can be transformed from one form to another. o ΔEsystem = - ΔEsurroundings the Second Law of Thermodynamics states that: o In every energy conversion, some energy is lost as heat (thermal energy). Energy always flows from “hot to cold” or from high energy source to low energy source. Chem 30 Thermochemistry 1 Chemistry 30 Thermochemistry Notes Endothermic Reactions In an endothermic reaction, the surroundings feel cooler. o Example Exothermic Reactions In an endothermic reaction, the surroundings feel warmer. o Example IMPORTANT REACTIONS o Photosynthesis o o Cellular Respiration o o Hydrocarbon Combustion o o Note: water vapour formed when in open system, liquid water formed when in closed system (bomb calorimeter). there are two fundamental types of energy: 1. ________________ the energy of motion 2. ________________ energy that is stored Chem 30 Thermochemistry 2 Chemistry 30 Thermochemistry Notes Fundamental forms of Energy o Kinetic energy is the energy of motion. o When there is a change in temperature, molecules speed up or slow down therefore there is a change in kinetic energy. o ex: when a gas is heated, the gas molecules increase their kinetic energy and as a result move faster o Heat = Thermal Energy = Kinetic Energy o When there is no change in temperature, like melting and evaporating there is a change in potential energy. changes in ________________________________ take place during chemical reactions when ____________________________________ ___________________________________________________ chemical bonds are sources of __________________ potential energy __________________ bonds ____________________ energy __________________ bonds ____________________ energy if the energy added to break the bonds is _________________ than the energy released when the new bonds are formed then the reaction is __________________________ eg) endothermic changes are designated as ________________________ since energy is being _______________ to the system if the energy added to break the bonds is _____________ than the energy released when the new bonds are formed then the reaction is _________________________ eg) Chem 30 Thermochemistry 3 Chemistry 30 Thermochemistry Notes exothermic changes are designated as _________________________ since energy is being ___________ by the system the amount of energy lost or gained is _________________________ __________________________________ to the amount of substances that react ie) if 100 g of a substance burning will release ___________________ energy compared to when 50 g of that same substance burns Chem 30 Thermochemistry 4 Chemistry 30 Thermochemistry Notes A2 Calculating Energy ________________________ is a measure of the ________________ ________________________________ of the particles of a substance the ________________ the particles are moving, the _____________ the temperature the amount of energy needed to heat a substance depends on three factors: 1. the ______________ of the substance 2. the ________________________________________________ 3. the ___________ of substance (heat capacity) _____________ heat capacity is heat required to change the temperature of ____________________ of a substance by _________ where: Q = heat energy in J m = mass in g Δt c = specific heat capacity in J/gC ***found on pg 3 of data booklet Example 1 Find the heat required to change 2.50 g of water from 10.0C to 27.0C. Example 2 200g of a liquid solvent is heated up by 10K, with 4240 J of energy. What is the specific heat capacity of the liquid? Workbook – PG 1 -2 All Qs Extra Practice – A1 & A2 Chem 30 Thermochemistry 5 Chemistry 30 Thermochemistry Notes A3 Enthalpy The total of the kinetic and potential energy within a chemical system is called its enthalpy. (Energy possessed by the system) changes in enthalpy are related to changes in energy however and occur whenever heat is released or absorbed in a physical, chemical or nuclear change … Which means that we can use energy change (Q) from the system to the surroundings to infer the change in enthalpy. Changes in Enthalpy (Δ) = Changes in Energy (Q) ΔrH = Q KJ = KJ Enthalpy change, ________, is measured in J or KJ subscripts are sometimes used to denote the type of process, for example “r” for “reaction” _________ = enthalpy of reaction the “” symbol is used to denote changes taking place at standard conditions _________ = standard enthalpy of reaction (at SATP 100 kPa and 25C) Molar enthalpy is the enthalpy change per mole of a substance molar enthalpy is designated as rHm or Hm molar enthalpy is measured in _____________________ Chem 30 Thermochemistry 6 Chemistry 30 Thermochemistry Notes Quick Practice/Concept Check If 2 moles of an unknown substance react and create 1200 J of energy, what is the molar enthalpy of reaction for that substance? Communicating Enthalpy Changes Exothermic Reactions 1. Total Enthalpy rH Notation the total enthalpy (heat) of reaction can be given as a rH value ________________ of the equation the sign on rH is _____________________ since the enthalpy of the system is ________________________ eg) 2. Molar Enthalpy rHm Notation the _____________________ (heat) of reaction can be given or determined from the balanced chemical equation or amount of substance. the sign on rH is negative in this cause communicating the enthalpy of the system is decreasing (exothermic) eg) Chem 30 Thermochemistry 7 Chemistry 30 Thermochemistry Notes 3. Total Enthalpy As a term Inside the Equation in an exothermic reaction enthalpy is included as a _______________ eg) 4. Potential Energy Diagrams shows the potential energy of the __________________ and the __________________ of a chemical reaction reactants have _____________ potential energy than the products in an exothermic reaction the difference between the reactants and products is the __________ Exothermic Products have__________ EP than the reactants energy has been ____________ to the surroundings Chem 30 Thermochemistry 8 Chemistry 30 Thermochemistry Notes During an exothermic reaction, the enthalpy of the system decreases and heat flows into the surroundings. We observe a temperature increase in the surroundings. Endothermic Reactions 1. Total Enthalpy rH Notation the sign on rH is ____________________ since the enthalpy of the system is __________________________ eg) 2. Molar Enthalpy rHm Notation the sign on rH is _________________ since the enthalpy of the system is increasing eg) 3. Total Enthalpy as a term Inside the Equation in an endothermic reaction enthalpy is included as a ______________ eg) Chem 30 Thermochemistry 9 Chemistry 30 Thermochemistry Notes 4. Potential Energy Diagrams reactants have ___________ potential energy than the products in an endothermic reaction the difference between the reactants and products is the ___________ Endothermic Products have _________ EP than the reactants energy has been ______________ by the system During an endothermic reaction, heat flows from the surroundings into the chemical system. We observe a temperature decrease in the surroundings. Chem 30 Thermochemistry 10 Chemistry 30 Thermochemistry Notes __________________-> energy is a product (right side of the equation)-> _____= negative __________________->energy is a reactant (left side of the equation)-> _____= positive Workbook - Communicating Enthalpy Questions PG 3-4 Extra Practice - A3 Communicating Enthalpy F. Calculating Enthalpy Changes molar enthalpy, in kJ/mol, and the number of moles of a substance can be used to calculate the enthalpy change of a phase change: where: H = n= rH = the number of moles can either come from the __________________ in the chemical reaction or from the formula always have a sign on H or H o ______________ for ___________________ (energy absorbed) o ______________ for ___________________ (energy released) Chem 30 Thermochemistry 11 Chemistry 30 Thermochemistry Notes Example 1 Calculate the molar enthalpy of combustion for oxygen given the following information: 2 C2H6(g) + 7 O2(g) 4 CO2(g) + 6 H2O(g) cH = 2856.8 kJ Example 2 Find the enthalpy change when 5.50 g of pentane burns. cH = 3244.8 kJ/mol Example 3 When methane is burned, oxygen is consumed. Determine the mass of oxygen consumed if the change in enthalpy is 250 kJ and the molar enthalpy of reaction for oxygen is 401.3 kJ/mol. Workbook Workbook Pg 5-6 All Qs Extra Practice – A3 Calculating Enthalpy Chem 30 Thermochemistry 12 Chemistry 30 Thermochemistry Notes A4 Calorimetry calorimetry is a technological process of _______________________ ________________________________________________________ the isolated system used to determine the heat involved in a phase change or in a chemical reaction is called a _____________________ Calorimeter Steps for Using a Simple Calorimeter 1. Measure the __________________________________ of the water in the calorimeter. 2. Add the ___________________ to the calorimeter. 3. Allow reaction to proceed, ________________ the solution to ensure even temperature. 4. Measure the __________________________________ of the water in the calorimeter (maximum temperature for exothermic reactions, minimum temperature for endothermic reactions) calorimetry is based on the First and Second Law of Thermodynamics…energy is conserved and energy is transferred from hotter objects to cooler objects until thermal equilibrium is reached it is assumed that _______________________ is ________________ ___________________________by the system except for the energy required or released by the _________________________________ Chem 30 Thermochemistry 13 Chemistry 30 Thermochemistry Notes calculations are based on the Principle of Heat Transfer: you must use a ____________ with you H values (either enthalpy change or molar enthalpy) endothermic = ___________________ value exothermic = ____________________value Example 1 A chemical reaction in a calorimeter causes the temperature of 500 g of water to increase in temperature from 10.0C to 52.0C. Calculate the heat released by this reaction. Give your answer in kJ. Example 2 An 8.40 g sample of N2(g) is reacted with pure oxygen in a bomb calorimeter containing 1.00 kg of water to produce N2O. The temperature of the water dropped by 5.82C. What is the molar heat of reaction of N2(g) in kJ/mol? Chem 30 Thermochemistry 14 Chemistry 30 Thermochemistry Notes Example 3 A student built a simple calorimeter with a 25.0 g tin can and 150 mL of water. Calculate the molar enthalpy of combustion of ethanol in kJ/mol if 0.166 g of this fuel increased the temperature of the calorimeter by 7.00C. Remember to include not only the heat gained by the water but also by the calorimeter. Example 4 A student mixes 100.0 mL of 0.500 mol/L HBr(aq) with 100.0 mL of 0.500 mol/L KOH(aq). The initial temperature of both solutions is 21.00C and the highest temperature reached after mixing is 24.40C. Calculate the molar enthalpy of neutralization in kJ/mol for the HBr(aq). Assume both solutions have the density and heat capacity of pure water. Workbook PG 14 All Qs Extra Practice - A4 Calorimetry Chem 30 Thermochemistry 15 Chemistry 30 Thermochemistry Notes A5 Hess’ Law: Predicting Enthalpy (rH) Changes because of the law of conservation of energy, the heat of reaction is the ______________ whether the reactants are converted to the products in a ______________________________________ or in a ______________________________________________________ G.H. Hess (1840) suggested that if two or more __________________ __________________________ are ______________ to give a final equation then the ________________________ can be added to give the _____________________________________________________ sometimes the heat of reaction for a chemical change is not easily measured due to time of reaction, cost, rarity of reactants etc. so we use Hess’s Law to calculate rH Steps: 1. Write the __________________________________, if it is not given. 2. ________________________ the given equations so they will ______ to yield the ______________________________________. if you multiply or divide an equation, multiply or divide the H by the ______________________________ if you flip an equation, __________ the sign on H 3. _________________ the reactants and products where possible to ______________________ (you must end up with your net equation!) 4. _________ the component enthalpy changes to get the ____________ ______________________________ Chem 30 Thermochemistry 16 Chemistry 30 Thermochemistry Notes Example 1 Find the enthalpy change and draw the EP diagram for C(s, di) C(s, gr) using the following reactions: C(s, gr) + O2(g) CO2(g) H = 393.5 kJ C(s, di) + O2(g) CO2(g) H = 395.4 kJ Example 2 Find the enthalpy change for H2O2(l) H2O(l) + ½ O2(g) using the following reactions: H2(g) + O2(g) H2O2(l) H = 187.8 kJ H2(g) + ½ O2(g) H2O(l) H = 285.8 kJ Chem 30 Thermochemistry 17 Chemistry 30 Thermochemistry Notes Example 3 Find the heat of reaction for C(s) + 2 H2(g) CH4(g) using the following reactions: C(s) + O2(g) CO2(g) H = 393.5 kJ H2(g) + ½ O2(g) H2O(l) H = 285.8 kJ CH4(g) + 2 O2(g) CO2(g) + 2 H2O(l) H = 890.5 kJ Workbook PG 9-11 All Extra Practice A5 Hess’s Law – Additivity of Reaction Heats Standard Heats of Formation fH sometimes it is not easy to measure the heat change for a reaction (too slow/expensive) in this case, H can be determined using _______________________ ____________________________________ heats of formation (fH) are the changes in EP that occur when ________________________________________________________ Hf for elements cannot be directly measured therefore they are designated as __________…all other fH values are in reference to this…see pages 4-5 in data booklet the fH is an indirect measure of the _____________________ of a compound the more ______________________________________________, the more ______________________________________________ (this means you have to add that energy to decompose it) Chem 30 Thermochemistry 18 Chemistry 30 Thermochemistry Notes eg) List the following compounds in order from most stable to least stable. H2O(l) fH = C2H4(g) fH = N2O4(g) fH = PCl3(l) fH = Al2O3(s) fH = Hess’s Law formula states that the ________ is the difference between the standard heats of formation of the __________________ and the _______________________ rH = Example 1: Calculate the standard heat of combustion for 2 CO(g) + O2(g) 2 CO2(g) and draw the EP diagram for this reaction. Chem 30 Thermochemistry 19 Chemistry 30 Thermochemistry Notes Example 2: Find the heat of combustion of ethane and draw the EP diagram for this reaction. The products of combustion are gases. Example 3 Calculate the molar enthalpy of combustion for ethane. The products of combustion are gases. Chem 30 Thermochemistry 20 Chemistry 30 Thermochemistry Notes Example 4 Calculate the energy released when 25.0 g of methanol is burned. The products of combustion are gases. Example 5 Calculate the molar heat of formation for ethylene glycol given the following information: (CH2OH)2() + 5/2 O2(g) 2 CO2(g) + 3 H2O() H = 1178.0 kJ Workbook PG 7-8 & 12-13 All Qs Extra Practice A5 Hess’s Law – Additivity of Reaction Heats Chem 30 Thermochemistry 21 Chemistry 30 Thermochemistry Notes A6 Energy and Efficiency most of Canada’s energy (electricity) comes from ________________ processes such as the combustion of ________________________ electricity is also generated through ____________________ processes both methods involve changing ________________________________ (a _________________ change) which turns turbines to generate electrical energy how does the energy from physical, chemical and nuclear processes compare: o __________________ changes involve the breaking and forming of ___________________________ forces (__________ kJ/mol) o _________________ changes involve the breaking and forming of ____________________________ (______________ kJ/mol) _______________ changes involve changes within the ______________________________________________ (___________________________________________ of kJ/mol) _____________________ is the ratio of _________________________ produced (energy _____________) to ___________________________ in its production (energy _____________) Chem 30 Thermochemistry 22 Chemistry 30 Thermochemistry Notes we have developed many technologies that help us to solve practical problems it is important to be as ____________________ as possible with appliances and vehicles saving energy _________________________________ and it helps to _____________________________________________ (greenhouse effect and acid rain) in any process, the __________________________________________ that take place, the ________________________________ the process because of ______________________ in transfer gas furnace (natural gas) is about __________ efficient since it is used to directly supply heat natural gas power plant is only about __________ efficient because there are several energy conversions that take place before electricity is generated (water to steam to kinetic energy to mechanical energy to electrical energy) Fuelling Society we must assess the _____________________________________ of relying on any fuel source when selecting an energy source, efficiency is not the only consideration the _____________________________________________ must also be considered Chem 30 Thermochemistry 23 Chemistry 30 Thermochemistry Notes Advantages vs. Disadvantages of Fossil Fuels Advantages Disadvantages _______________ processes _______________ produce ___________ _____________________ but they do produce ___________________ ______________________ which lasts for thousands of years _________ turbines use a ______________________ energy source (sun indirectly) but are not free of problems…they are _____________ ___________________________________________________ ______________________ power is also ____________________ but damming rivers _________________________________________ on both sides of the dams the amount of ____________ released by a fuel determines how __________________ it is fuels that use renewable energy sources (________________________ _________________________________________ etc.) and nuclear power are considered the ________________________ ___________________ is the _____________ fossil fuel and _______ is the ____________________________ regardless of which source of energy we use, we must think about the impact that our fuels have on the environment Your Assignment: Chem 30 Thermochemistry WB: PG 15 Q 3 (a,b,c) 24 Chemistry 30 Thermochemistry Notes A7 Bond Energy and Activation Energy bond energy is the energy ___________________________________ ___________________________ or the energy __________________ _______________________________________________________ the ________________________________________________ of a reaction represents the _____________________________ from _________________ the bonds in the reactant(s) and _____________ the bonds of the product(s) in _________________________ reactions, bond breaking absorbs ___________ energy than the bond formation gives off, resulting in a ____________ Exothermic: H2(g) + Cl2(g) 2 HCl(g) + energy Energy (kJ) Reaction Progress Chem 30 Thermochemistry 25 Chemistry 30 Thermochemistry Notes in _______________________ reactions bond breaking absorbs ___________ energy than the bond formation gives off, resulting in a ___________ Endothermic: 2 H2O() + energy 2 H2(g) + O2(g) Energy (kJ) Reaction Progress the energy barrier that must be overcome for a chemical reaction to occur is called the _____________________________________ the atoms in the ________________have to be __________________ in order for them to bond in a different configuration and become the products the activation energy is always ______________ than the energy contained in the reactants and the products, however the amount of activation energy necessary is dependent on the reaction the __________ of the activation energy barrier on a potential energy diagram represents the _________________________________ of the reaction in both endothermic and exothermic reactions, the molecules of the reactants are moving with a certain amount of ___________________ _______________________ Chem 30 Thermochemistry 26 Chemistry 30 Thermochemistry Notes when the reactants _______________ with each other, the kinetic energy is transformed into _____________________________ this potential energy is then stored in bonds of the chemical species that exists at the top which is called the ________________________ this is a transitional species that is neither a reactant nor a product which has _________________________________ and is ______________________________________ when the partial bonds of the activated complex re-form as chemical bonds in the products, the stored potential energy is converted back into __________________________________ as the product molecules _____________________________ Chem 30 Thermochemistry 27 Chemistry 30 Thermochemistry Notes Potential Energy Diagram: Exothermic Potential Energy Diagram: Endothermic * * EP (kJ) EP (kJ) Reaction Progress Reaction Progress * A8 Energy Diagrams and Catalysts a catalyst is a substance that _________________________________ of a chemical reaction ______________________________________ by the reaction catalysts provide ________________________________ for chemical reactions they ____________ the _______________________________ required for a reaction to take place which results in the production of a _____________________________________ of products in a given length of time (even at a lower temperature) catalyzed reactions can be shown on EP diagrams: Potential Energy Diagram: Exothermic Potential Energy Diagram: Endothermic EP (kJ) EP (kJ) Chem 30 Thermochemistry Reaction Progress 28 Reaction Progress Chemistry 30 Thermochemistry Notes Catalysts in Industry catalysts are often used in industry to speed up the reactions and obtain a reasonable reaction rate under reasonable conditions in cars, we have ________________________________ that use Pt(s), Pd(s) and Rh(s) to speed up the combustion of exhaust gases so that more of the products are _________________ (_______ instead of ______, _______ instead of ______) the oil and gas industry uses catalysts (Pt(s), HF(aq), H2SO4(aq) etc) in the ______________________________________________ of _____________________ and _________________ to make more marketable fuels like gasoline Enzymes compounds that act as catalysts in living systems are called __________________ called ________________________ catalysts chemical reactions in the body occur at very _______ temperature (37C) and without catalysts many would be too ___________ Your Assignment: WB: PG 17-18 All Qs Extra Practice: Extra Practice Chem 30 Thermochemistry 29