Thermochemistry
Topic: Specific Heat and Calorimetry Unit: Thermochemistry Topic: Specific Heat and Calorimetry Objectives: Day 1 of 3 To understand specific heat and it’s units To understand calorimetry and and the equation q = (m)(Cp)(ΔT) To understand the difference between endo and exothermic changes To understand the first law of thermodynamics
Heat Transfer & Specific Heat If you recall, heat is the energy transferred between objects that have different temperatures Heat is always transferred from an object with a higher temperature to an object with a lower temperature Temperature is a measure of the average kinetic energy
What is Heat? The transfer of kinetic ______from a hotter object to a colder object When heat is abosrbed molcules move more _______ energy rapidly Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer Joules rapidly
Heat Transfer & Specific Heat The temperature change of an object depends on: The amount of heat that is transferred to or from the object The mass of the object The specific heat of the object
Specific Heat Specific heat is the amount of heat needed to raise the temperature of 1 gram of a substance by 1ºC We represent specific heat with symbol (Cp) It is a constant for a given substance at a certain pressure The units of specific heat are (J/g•ºC) Where J is the SI unit for energy, the joule (J)
Specific Heat Think of specific heat as how much heat a substance can hold Substances with a high specific heat act like a “heat sponge” They can absorb a lot of heat with just a small change in temperature
What is specific heat? The amount of ______needed to raise the temperature of 1 _____ of a substance by ___ºC It is symbolized by the symbol Cp It is a constant for a given substance at a certain pressure Units are in (J/g•ºC) heat gram 1 Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer joules
Calorimetry Calorimetry is the measure of heat transfer Suppose a chemist want s to calculate the amount of heat transferred when the temperature of a sample changes by so many degrees The amount of heat absorbed or released by a sample is symbolized by the letter q It is calculated using the following equation: q = (m)(Cp)(ΔT)
What is calorimetry? A measure of heat _______ given by the equation: q = (m)(Cp)(ΔT) transfer Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer joules
q = (m)(Cp)(ΔT) Calorimetry Here is what each symbol means for the equation: q = (m)(Cp)(ΔT) q is the symbol for heat If q is positive heat is absorbed by the system & the reaction is endothermic M is the mass of the sample in grams Cp is the specific heat of the Substance it is a constant q = (m)(Cp)(ΔT) If q is negative heat is lost by the system & the reaction is exothermic ΔT is the change in temperature
Calorimetry If energy flows into the system (endothermic) q is positive(+) On the other hand if energy is flowing out of the system (exothermic) q is negative(-) Surroundings System Energy Surroundings Surroundings Surroundings System Energy Surroundings Surroundings
What is the difference between endo- and exothermic changes? An endothermic change ______ heat (q+) and energy flows ____the system An exothermic change releases heat (q-) and energy flows out of the_____ absorbs into Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer joules system
The energy in the universe is constant Thermodynamics The study of energy is called thermodynamics The law of conservation of energy is often called the first law of thermodynamics and is stated as follows: The energy in the universe is constant
What is the First Law of Thermodynamics? The First Law of Thermodynamics states that the energy in the universe is________ constant Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer joules
Thermodynamics The same is true for w If the system does work on the surroundings (energy flows out of the system) w is negative If the surrounding do work on the system (energy flows into the system) w is positive Surroundings Surroundings System System Energy Surroundings Energy Surroundings Surroundings Surroundings
Practice: Use the equation q = (m)(Cp)(ΔT) and Solve for q What amount of heat is needed to increase the temperature of 2006 grams of Mercury (Hg) by 7.5ºC? The specific heat of mercury is 0.139 J/g•ºC. Use the equation q = (m)(Cp)(ΔT) and Solve for q q = (m)(Cp)(ΔT) q = (2006 g)(0.139 J/g•ºC)(7.5ºC) q = 2090 Joules
First Law of Thermodynamics The First Law of Thermodynamics states that the energy in the universe is constant This is another way of stating the law of conservation of energy
The First Law of Thermodynamics Suppose you want to measure the amount of heat transferred from a hot piece of metal (system) to a sample of cooler water (surroundings) If you know the specific heat of water, the water’s mass and the water’s temperature change, you can calculate the amount of heat absorbed by the water This equals the amount of heat released by the metal System Surroundings System
Practice: A 118 gram piece of tin at 85ºC is dropped into a 100 grams of water at 35ºC. The final temperature of the mixture is 38ºC The specific heat of water is 4.18 J/g•ºC What amount of heat is absorbed by the water? What amount of heat is released by the tin? What is the specific heat of tin? Solving for the specific heat of water we get: q = (100g)(4.18 J/g•ºC)(3.0ºC) = 1254 J The value is positive (+) because heat is absorbed This same amount of heat is released by tin, and when heat is released the q value is negative (-) qwater = -qtin 1254 J = -1254 J
(system surroundings) Visualize: What is hotter, the water or piece of tin? In which direction will heat move? Heat moves from the metalTo the water (system surroundings) qwater Is positive (+) heat is gained qmetal Is negative (-) heat is lost 100 grams of water at 35o Celsius System Surroundings 118 gram piece of tin at 85o Celsius System
Practice: A 118 gram piece of tin at 85ºC is dropped into a 100 grams of water at 35ºC. The final temperature of the mixture is 38ºC The specific heat of water is 4.18 J/g•ºC Because the same amount of heat that is absorbed by water is also released by tin, we can use 1254 J for to solve for the amount of heat released by tin However when heat is released, it’s value is negative and we get -1254 J, So, the amount of heat released by tin is -1254 J Substituting -1254 in for q, we can solve for specific heat (Cp) qtin = -1254 J = (118g)(Cp)(-47ºC) Cp = -1254 (118g)(-47ºC) Cp = 0.23 J/g•ºC
Summarize: In the equation, q = (m)(Cp)(ΔT), q represents the heat ____or_____, m is the ____ in grams, Cp is the _____heat, and ΔT is the change in _____ An endothermic change ______ heat (q+) and An exothermic change ______heat (q-) In the last practice problem the amount heat lost by the ____ is equal to the amount of heat ______by the water (Or q = -q) Answer Bank gram Mass gained Absorbs releases temperature specific metal system lost
Topic: Enthalpy and Reaction Rates Unit: Thermochemistry Topic: Enthalpy and Reaction Rates Objectives: Day 2 of 2 To understand enthalpy and how it applies to a reaction To understand how reactions proceed and the factors that effect them
Enthalpy So far we have seen that some reactions are exothermic and other reactions are endothermic Chemists also like to know exactly how much energy or heat is produced or absorbed by a given reaction We will use the term enthalpy to describe the change in heat that occurs during a reaction ΔH = Heat
Enthalpy Enthalpy (H) is the amount of heat a sample has at a certain temperature and pressure It is the sample’s heat content Enthalpy cannot be measured, only changes in enthalpy can be measured As a reaction takes place and atoms are rearranged, heat is either released or absorbed
What is Enthalpy? Enthalpy (H) is the amount of ______a sample has at a certain temperature and pressure Think of it as a sample’s heat______ heat Answer Bank enzyme released Content activation Absorbed minimum products Heat chemical content
Enthalpy The change in heat that takes place during a reaction is called the heat of reaction (ΔH ) It is the amount of heat released or absorbed in a chemical reaction, given 1 mol of a reactant or product ΔHrxn is the difference between enthalpy of the reactants and products In other words, ΔHrxn = (H of products) – ( H of reactants)
What is the heat of reaction? The amount of heat _______or _______ in a chemical reaction, given 1 mol of a reactant or product represented by ΔH Where ΔHrxn = (H of______ ) – ( H of reactants) absorbed released Answer Bank enzyme released Content activation Absorbed minimum products Heat chemical products
Practice: Classify the reactions below as wither exo- or endothermic: CaCO3 CO2 + CaO ΔHrxn = +178.4 kJ/mol CaCO3 ΔHrxn is positive so the reaction is endothermic Reaction 2 = _______________ CH4 + 2O2 CO2 + 2H2O ΔHrxn = -890.2 kJ/mol CH4 ΔHrxn is negative so the reaction is exothermic
The negative sign indicates an exothermic process Practice: When 1 mol of methane is burned at constant pressure, -890 kJ of energy is released as heat. Calculate ΔH for a process in which a 5.8 gram sample of methane is burned at constant pressure First convert grams to moles using the molar mass of methane 16 g/mol, then use our conversion factor of -890 kJ/mol q = ΔH = -890 kJ/mol CH4 The negative sign indicates an exothermic process kJ/mol is our conversion factor 5.8 g CH4 1 mol CH4 -890kJ = -320 kJ CH4 16.0 g CH4 1 mol CH4
The negative sign indicates an exothermic process Practice: 2SO2+O2 2SO3 ΔHrxn = -98.9 kJ/mol SO3 Consider the above equation: If 8.9 mol of SO2 reacts with excess oxygen, how much heat is released? We are given the ΔH for SO3 So, we need to use our mol ratio to go from mol of SO2 to mol SO3 ΔHrxn = -98.9 kJ/mol SO3 The negative sign indicates an exothermic process kJ/mol is our conversion factor 8.9 mol SO2 2 mol SO3 -98.9kJ = -880.2 kJ SO3 2 mol SO2 1 mol SO3
Enthalpy and Reaction Rates A change in energy always accompanies a reaction whether positive or negative The diagram to the right illustrates how energy changes from reactants to products The activation energy is the minimum energy needed for the reaction to take place Once the activation energy is met, the reaction can proceed
Enthalpy and Reaction Rates A common analogy is pushing a boulder over a hill. Actually over a "pass" . The reactants are on one side like the boulder. The energy needed to push the boulder to the crest of the hill is like the activation energy. The products are like the condition when the boulder is at the bottom of the far side of the "pass".
What is Activation Energy? The _________energy needed for the reaction to take place minimum Answer Bank enzyme released Content activation Absorbed minimum products Heat chemical
minimum amount of energy EA= Activation energy minimum amount of energy needed for a chemical reaction to take place EA Products Energy ΔH Reactants Reaction Rate (time) ΔH = The amount of heat released or absorbed in a chemical reaction (heat change)
minimum amount of energy EA= Activation energy minimum amount of energy needed for a chemical reaction to take place Products C6H12O6 + O2 EA ΔH = 1274.5 endothermic (+) Energy Reactants H2O + CO2 Reaction Rate (time)
minimum amount of energy EA= Activation energy minimum amount of energy needed for a chemical reaction to take place Reactants CH4 + O2 ΔH = -890 exothermic (-) Energy Products CO2 + H2O Reaction Rate (time)
Catalyst In order to lower the activation energy, some reactions utilize what’s know as a catalyst By lowering the activation energy, a catalyst (substance) accelerates a chemical reaction without itself being affected
Catalyst A catalyst is a substance that lowers the activation energy and accelerates a chemical reaction without itself being affected A biological catalyst is called an enzyme Enzymes help orientate molecules or atoms in specific manner so they are more likely to react Your body has millions of enzymes!!
What is a catalyst? A substance that lowers the _______energy and ________ a reaction without itself being affected or consumed in the reaction A biological catalyst is called an _____ activation accelerates Answer Bank enzyme released Content activation Absorbed minimum products Heat Chemical accelerates enzyme
Check For Understaning Is the reaction endothermic or exothermic? 1= 2= 3= 4= Answer Bank Products Activation energy Reactants Heat of reaction ∆H
Summarize: Review: ______ is a measure of the average kinetic energy of a molecular motion As heat is added, molecules move ______ The amount of heat released or absorbed in a chemical reaction is the _____ of reaction A substance that lowers the activation energy is called a _____ Draw & Label the diagrams below: Answer Bank catalyst faster activation products Heat temperature Energy Reaction Rate (time) Reactants H2O + C O2 Products C6H12O6 + O2 ΔH = +1274.5 endothermic (+) EA Energy Reaction Rate (time) Reactants CH4 + O2 Products CO2 + H2O EA= Activation energy ΔH = - 890 exothermic (-)
Topic: Heat Temperature & Kinetic Energy Unit: Thermochemistry Topic: Heat Temperature & Kinetic Energy Objectives: Day 3 of 3 To understand the relationship between heat and kinetic energy To understand the relationship between heat and intermolecular forces between molecules
Temperature and Kinetic Energy If you recall, temperature is measure of the average kinetic energy of the atoms or molecules In other words as heat is absorbed, molecules move more rapidly At 0 Kelvin all molecular motion will cease
What is the relationship between temperature and kinetic energy of molecules??? As temperature ________, so does kinetic energy, or the _____ at which molecules move At 0 Kelvin (-273 Co) all molecular motion will ____ increases Answer Bank Increases(2) rate Decreases(2) stop rate stop
Intermolecular Forces In the solid state, molecules are held together by strong intermolecular forces In order to overcome these forces, heat or energy must be added into the system will occur, LIQUIDGAS As more heat is added, intermolecular forces are overcome and a phase change occurs SOLIDLIQUID And if even more heat is added, another phase change will occur, LIQUIDGAS
Intermolecular Forces Conversely, if we remove the heat or energy, intermolecular forces will take over and the gas will become a liquid GASLIQUID If even more heat is removed, another phase change will occur and a the liquid will become a solid LIQUIDSOLID
At a certain temperature (1000C) Water becomes If we continue to add heat, the Temperature Of the steam will rise At a certain temperature (1000C) Water becomes steam and once again the temperature stabilizes. Molar Heat of Vaporization This is the H vaporization The energy required to change one mol of a liquid into vapor The energy required to melt 1 mole of ice into water At a certain temperature (00C) the ice melts and becomes water, The temperature stabilizes. This is the Molar Heat of Fusion H fusion Now that the ice has melted, the temperature of the water continues to rise Temperature rises as we add heat
What’s the relationship between heat and the intermolecular forces holding molecules together??? Answer Bank Increases(2) rate Decrease(s)(2) stop As a substance like water is heated, heat ______ and intermolecular forces _______. As a substance like water is cooled, heat ______ and intermolecular forces increase. increases decrease decreases
Empirical Formula Empirical Formula - A formula that gives the simplest whole-number ratio of atoms in a compound. For example: If carbon and hydrogen are present in a compound in a ratio of 1:2, the empirical formula for the compound is CH2.
minimum amount of energy Reaction Rate (time) Reactants H2O + C O2 Products C6H12O6 + O2 EA= Activation energy minimum amount of energy needed for a chemical reaction to take place ΔH = 1274.5 endothermic (+) EA Energy Reaction Rate (time) Reactants CH4 + O2 Products CO2 + H2O EA= Activation energy ΔH = -890 exothermic (-)