Thermochemistry.

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 the equation q = (m)(Cp)(ΔT) To understand the difference between endo and exothermic changes To understand the first law of thermodynamics

Quickwrite: Answer one of the question below in 1-2 sentences:
How do you think heat travels from your body to your surroundings? What do you think holds heat better, water or a metal such as Iron?

Heat Transfer & Specific Heat
If you recall, heat is the energy transferred between objects that have different temperatures Heat is kinetic energy that 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 of the atoms or molecules

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), g is the mass in grams and C is degrees Celsius Think of specific heat as a substance or chemicals ability to hold and retain heat 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 heat needed to raise the temperature of 1 gram of a substance by ___ºC Symbolized by Cp Units are in (J/g•ºC) Think of it as how well a substance can hold or release heat 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)

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= Tfinal -Tinitial

What is calorimetry? A measure of heat _______ given by the equation: q = (m)(Cp)(ΔT) q = heat transferred in joules m= mass of sample in grams Cp = specific heat ΔT = Tfinal – Tinitial = change in temperature in degrees Celsius Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer joules

Calorimetry If energy or heat 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 into the system An exothermic change releases heat (q-) and energy flows out of the_____ Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer joules

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________ Answer Bank Gram Absorbs into Energy constant Heat system Colder 1 transfer joules

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 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

Practice: Use the equation q = (m)(Cp)(ΔT) and Solve for q
How much heat in is required to raise the temperature of 150 grams of water from 35°C to 75°C? (CH20= J/g°C) Use the equation q = (m)(Cp)(ΔT) and Solve for q q = (m)(Cp)(ΔT) q = (150g)(4.184 J/g•ºC)(75ºC - 35ºC) q = (150g)(4.184 J/g•ºC)(40 ºC) q = 25,104 Joules

Hot 50 gram sample of Iron at 100OC
Lab Scenario We know q = (m)(Cp)(ΔT) This gives us the equation: So -qmetal is negative because the metal is losing heat qwater is positive because it is gaining heat According to the first law of thermodynamics, the heat lost by the metal must be equal to heat gained by the water or qwater = -qmetal Consider the following scenario: Lets say you have 100 grams of water at 25oC Then you drop a 50 gram piece of metal Iron into the water How is heat transferred? Heat flows from the hot piece of metal to the surrounding water Hot 50 gram sample of Iron at 100OC (mwater)(Cwater)(ΔTwater) = (mmetal)(Cmetal)(ΔTmetal) Thermometer 100 grams of water = 100ml of water at 25OC

Specific heat and mass values
Practice: A 50 gram sample of Iron at 100ºC is dropped into 100 grams of water at 21ºC. The final temperature of the mixture is 25ºC. What is the specific heat of Iron?(CH20= J/g°C) Heat lost by the metal = heat gained by the water, In other words, -qmetal = qwater (negative because the metal is losing heat) We also know q = (m)(Cp)(ΔT) which gives us the equation (mwater)(Cpwater)(ΔTwater)= (mmetal)(Cpmetal)(ΔTmetal) Lets consider what we know: mwater= 100 gms Cpwater= J/g°C ΔTwater= 25°C - 21°C = 4°C mmetal= 50 gms Cpmetal= ??????? ΔTmetal = 25°C - 100°C = - 75 °C (100 gms)(4.184 J/g°C)(4 °C) = (50 gms )(Cmetal)(75°C) (100 gms)(4.184 J/g°C)(4°C) = Cmetal Solving for specific heat (Cmetal ) we get: Cmetal = 0.45 J/g°C Specific heat and mass values cannot be negative!!!! (50 gms )(75 Co)

Practice: A 62.1 gram piece of metal is heated to 100° C and placed in a calorimeter with 100 mL of water. If the water in the calorimeter rises from 21°C to 32°C, (final temperature of the mixture is 32°C) what is the specific heat of the metal? (CH20= J/g°C) 1 mL of water = 1 gram of water Heat lost by the metal = heat gained by the water, In other words, -qmetal = qwater (negative because the metal is losing heat) And we know q = (m)(Cp)(ΔT) so that gives us the equation (mwater)(Cpwater)(ΔTwater)= (mmetal)(Cpmetal)(ΔTmetal) Substituting in our values we get: mwater= 100 gms Cpwater= J/g°C ΔTwater= 32°C - 21°C = 11 °C mmetal= 62.1 gms Cpmetal= ??????? ΔTmetal = 32°C - 100°C = - 68 °C

Summarize: In the equation, q = (m)(Cp)(ΔT), explain what each variable represents: Compare and contrast endothermic heat changes with exothermic heat changes

Topic: Enthalpy and Reaction Rates
Unit: Thermochemistry Topic: Enthalpy and Reaction Rates Objectives: Day 2 of 3 To understand enthalpy and how it applies to a reaction To understand how reactions proceed and the factors that effect them To understand the difference between endothermic and exothermic reaction coordinates

In every chemical reaction atoms are rearranged. But what else is do you think is released or absorbed during a chemical reaction? When you light your Bunsen burners, is this an endo- or exothermic reaction? Why do you think chemists would want to know how much heat is released or absorbed during a chemical reaction?

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______ Answer Bank enzyme released Content activation Absorbed minimum products Heat chemical

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 If is ΔHrxn is negative(-), the reaction is exothermic If is ΔHrxn is positive (+), the reaction is endothermic

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 If ΔH is positive the reaction is endothermic, if ΔH is negative the reaction exothermic Answer Bank enzyme released Content activation Absorbed minimum products Heat chemical

Practice: Classify the reactions below as either exo- or endothermic:
CaCO3  CO2 + CaO ΔHrxn = kJ/mol CaCO3 ΔHrxn is positive so the reaction is endothermic Reaction 2 = _______________ CH4 + 2O2  CO2 + 2H2O ΔHrxn = 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 = 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 = 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 = 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 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 Heat/Energy ΔH Reactants Reaction Rate (time) ΔH = The amount of heat released or absorbed in a chemical reaction (heat change)

EA= Activation energy minimum amount of energy needed for a chemical reaction to take place Products C6H12O6 + O2 EA ΔH = endothermic (+) Heat/Energy Reactants H2O + CO2 Reaction Rate (time)

EA= Activation energy minimum amount of energy needed for a chemical reaction to take place Reactants CH4 + O2 ΔH = -890 exothermic (-) Heat/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 _____ Answer Bank enzyme released Content activation Absorbed minimum products Heat Chemical accelerates

Check For Understaning
Is the reaction endothermic or exothermic? 1= 2= 3= 4= Answer Bank Products Activation energy Reactants Heat of reaction ∆H

__________________________
Reactants Fe2O3 + Al Energy Reaction Rate (time) Reactants __________________________ Products Products Al2O3 + Fe ΔH = kJ exothermic (-)

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 = endothermic (+) EA Energy Reaction Rate (time) Reactants CH4 + O2 Products CO2 + H2O EA= Activation energy ΔH = exothermic (-)

Topic: Heat Temperature & Kinetic Energy
Unit: Thermochemistry Topic: Heat Temperature & Kinetic Energy Objectives: Day 3 of 3 To learn the difference between intermolecular forces, dipole-dipole attraction, and hydrogen bonding To understand the relationship between heat and kinetic energy on a molecular level To understand the relationship between heat and intermolecular forces in the solid, liquid, and gas phases of matter

What do you think holds water molecules together? On the atomic or molecular level, how do you think the addition of heat effects atoms or molecules? What do you think is at a higher state of energy, water as steam (GAS), or, water as Ice (SOLID) Review: Is ice melting a physical or chemical change? In other words, is Ice still H2O after it melts? If you remove heat from water, which state of matter will water become? (Solid, Liquid, Gas……)

States of Matter GAS If you recall, there are there are 3 basic states of matter: SOLID, LIQUID, GAS In a GAS state, the atoms/molecules are in a higher energy state If we cool a GAS, (remove energy), a LIQUID state will arise And if we continue to cool the liquid, or remove energy, a SOLID state will eventually arise Conversely, if we add energy or heat, the opposite is true Remove Energy Add Energy LIQUID Remove Energy Add Energy SOLID

Intermolecular Forces
In order to change between states of matter(SOLID,LIQUID, GAS) certain forces must be overcome We call these forces, intermolecular forces, OR, the forces between atoms or molecules If you recall, many atoms are polar with charges on them, both positve(+) and negative(-) These positive and negative forces both ATTRACT and REPEL each other Notice, OPPOSITE charges attract, while LIKE charges repel + - + - + - + - + - + - = ATTRACTION = REPULSION

What are Intermolecular Forces?
Answer Bank Increases(2) attract Decreases(2) stop Forces that occur between molecules Opposite Charges _____, while like charges repel

Dipole-Dipole Forces in Water
Water is a POLAR molecule As a liquid, water is held together by the attractive forces between its slight positive and negative charges Water Molecules actually move and position themselves to take advantage of their positive and negative forces When water molecules line up and position themselves to take advantage of their charges, we call this dipole-dipole attraction H O - + H O - + H O - +

What is Dipole-Dipoles Attraction?
Answer Bank Increases(2) charges Decreases(2) stop When Molecules move and position themselves to take advantage of their ______

Hydrogen Bonding H O - + When enough energy is removed from water, it freezes For example, It explains why Ice freezes and even floats! Because the dipole-dipole forces are so strong in water, we give it a special name—HYDROGEN BONDING Hydrogen Bonding explains why water has such a high boiling point! It takes a lot of energy to overcome the intermolecular forces! = Hydrogen Bonding

- - - - - - - Hydrogen Bonding + + + + + + +
Hydrogen Bonding even explains the physical process or freezing When enough energy or heat is removed, water molecules actually spread apart and arrange themselves in a network so that their charges attract each other This creates a crystalline structure This is why Ice floats and is less dense that water H O - + O - H + O - H + O - H + H + O - O - H + = Hydrogen Bonding

What is Hydrogen Bonding?
Answer Bank Increases(2) rate Decreases(2) boiling A special type of Dipole-dipole attraction that explains why water has such a high ______ point, and; why ice floats and is less dense than water

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 As more heat is added, intermolecular forces are overcome and a phase change occurs SOLIDLIQUID And if even more heat is added, another phase change will occur, LIQUIDGAS

Conversely, if we remove the heat or energy, intermolecular forces will take over and the gas will become a liquid GASLIQUID If even more heat is removed, another phase change will occur and a the liquid will become a solid LIQUIDSOLID

Notice, temperature is constant and not changing or increasing during a phase change Why? because energy is being used to overcome the intermolecular attraction forces during a phase change Once a phase change has occurred, heat can now be absorbed by the system and molecules begin vibrating faster, that is they have a higher kinetic energy

At a certain temperature (1000C) Water becomes
If we continue to add heat, the Temperature Of the steam will rise Now that the ice has melted, the temperature of the water continues to rise As the molecules Move faster (kinetic energy increases) At a certain temperature (1000C) Water becomes steam and once again the temperature stabilizes. because the Energy is being Used To overcome the intermolecular forces to go From a LIQUIDGAS At a certain temperature (00C) the ice melts and becomes water, The temperature Stabilizes because The Energy is being used To overcome the intermolecular forces to go from a SOLID  LIQUID Temperature rises as we add heat because the molecules in the ice begin to move faster

What’s the relationship between heat and the intermolecular forces holding atoms or molecules together??? As a substance like water is heated, heat ______ and intermolecular forces are _______, resulting in a phase change (solid  liquid). As a substance like water is cooled, heat ______ and intermolecular forces take over resulting in a phase change (liquidsolid). During a phase change temperature is constant because energy is being used to overcome the intermolecular forces of the atoms or molecules Answer Bank Increases(2) Rate decreases overcome stop

Summarize: Explain intermolecular forces in your own words:
What is the difference between dipole-dipole attraction and hydrogen bonding? Explain the relationship between heat and intermolecular forces during a phase change for water: Explain why temperature remains constant during a phase change and increases after a phase change

Thermochemistry.

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