Thermochemistry CHAPTER 17.

Slides:



Advertisements
Similar presentations
Energy Transformations Thermochemistry is the study of energy changes that occur during chemical reactions and changes in state. The energy stored in the.
Advertisements

Chapter 17 Energy and Rate of Reactions.  Thermochemistry – study of the transfer of energy as heat that accompanies chemical reactions and changes 
Chapter 17 Thermochemistry and Kinetics. Thermochemistry – study of transfer of energy as heat that accompanies chemical reactions and physical changes.
Thermodynamics – chapter 17 Organic Chemistry –chapters 22 & 24
Thermodynamics and what it means to you.  Energy: Ability to do work or produce heat  First Law of Thermodynamics: Law of conservation of energy  Heat:
Chapter 17 Thermochemistry.
Unit 13: Thermochemistry Chapter 17 By: Jennie Borders.
The Flow of Energy. Think about this question for 15 seconds… What does a thermometer measure? Discuss with your neighbor what your answer is Share what.
THERMO- CHEMISTRY Thermochemistry Study of the heat changes that occur during a chemical reaction.
Unit 13: Thermochemistry Chapter 17 By: Jennie Borders.
Thermochemistry. Thermochemistry is concerned with the heat changes that occur during chemical reactions. Can deal with gaining or losing heat.
CHAPTER 17 THERMOCHEMISTRY. ENERGY Energy is the capacity to do work or to supply heat. Various forms of energy include potential, kinetic, and heat.
Good Morning 11/16/2015 Today we will be working on the notes for ch 11.
Chapter 15 Energy and Chemical Change Energy Energy can change for and flow, but it is always conserved.
Energy The ability to do work or produce heat The ability to do work or produce heat Potential- Stored energy Potential- Stored energy Energy stored in.
Thermochemistry Some Like It Hot!!!!!. The Flow of Energy ► Thermochemistry – concerned with heat changes that occur during chemical reactions ► Energy.
Chemistry Unit 8 Thermochemistry Chapter The Flow of Energy Energy Transformations – Goal 1 Chemical Potential Energy Energy stored in chemical.
THERMOCHEMISTRY. Law of conservation of energy Energy can be neither created or destroyed but can be converted from one form to another. Energy in = Energy.
TO LIVE IS THE RAREST THING IN THE WORLD. MOST JUST EXIST. THAT IS ALL.
Chapter 15 Energy and Chemical Change Section 15.1 Energy Section 15.2Heat Section 15.3Thermochemical Equations Section 15.4 Calculating Enthalpy Change.
Unit: ENERGY Topic 1: Types of Energy Energy = The ability to do work or produce heat Unit of energy = the Joule = J Two types: Potential Kinetic Lord.
Kinetics. is the branch of chemistry that is concerned with the speed of a chemical reactions( reaction rates) and the way in which reactions occur (reaction.
Thermochemistry: Energy and Heat The Nature of Energy u Energy is the ability to do work or produce heat. u It exists in two basic forms, potential energy.
Thermochemistry.
Phases of Matter, Bonding and Intermolecular Forces
Energy and Chemical Change
Thermodynamics Chapters 16 and 13.
THERMOCHEMISTRY.
Specific Heat.
The Flow of Energy Measuring and expressing enthalpy changes
Topic: Matter & Energy Aim: How can the amount of energy gained or lost by a system be calculated? Do Now: What Celsius temperature is the equivalent of.
Thermochemistry Chapter 11 Unit 12
Kinetics.
Thermochemistry.
THERMOCHEMISTRY.
Ch. 17 THERMOCHEMISTRY 1.
Liquids and Solids.
UNIT 3: ENERGY.
Chemical Thermodynamics
Heat and Chemical Change
Thermochemistry.
Unit 6: Physical Behavior of matter
Tuesday… HMWK: Eat, Sleep, relax and repeat… THEN…
Chapter 17 Review “Thermochemistry”
Thermochemistry Chapter 10.
You must turn in your notes
Reaction Energy.
Energy Transformations
How are they related? Chemistry and Energy.
Chapter 16 – Reaction Energy
Thermochemistry Unit 10 Lesson 2.
Unit 8: Thermochemistry
Thermochemistry CHAPTER 17.
CHEMISTRY Matter and Change
How are various forms of energy different?
Calculating Energy Changes at Phase Changes
Energy.
Thermochemistry.
Calculating Energy Changes at Phase Changes
Calculating Energy Changes at Phase Changes
Thermochemistry & Phases Test
Thermochemistry Chapter 16.
Calculating Energy Changes at Phase Changes
What is energy? Two types: Potential and Kinetic Page 2
Phases of Matter, Energy and Phase Changes
7.2 Thermochemistry Objective 2
Thermochemistry Chapter 17.
Thermochemistry Chemistry One B.
Do Now: Just to review before we start…
Presentation transcript:

Thermochemistry CHAPTER 17

Thermochemistry Thermochemistry: study of energy changes During chemical reactions During phase changes

How does Heat differ from Temperature? Temperature: average kinetic energy of particles The faster the particles are moving, the higher the temperature. Heat (q): transfer of kinetic energy Heat flows from high temp  low temp Units: Joules (SI unit) or calories (kCal = Cal in foods) 1 calorie = 4.184 J

Joule/Calorie Conversion Practice Example: 9.6 calories = ______ Joules 450 Joules = ______ calories 53 calories = ______ Joules 0.9 Joules = _______ calories 9.6 calories 4.184 Joules = 40.2 Joules 1 calorie 107.5 221.8 0.22

Energy Changes in Chemical Reactions Exothermic Reactions – give off energy A + B  C + D + energy Endothermic Reactions – absorb energy energy + A + B  C + D

Endothermic or Exothermic? Reactants  Products + Energy Reactants + Energy  Products 2NaHCO3 (s) + 129 kJ  Na2CO3 (s) + H2O (g) + CO2 (g) CaO (s) + H2O (l)  Ca(OH)2 (s) + 65.2 kJ baking bread campfire burning fuel photosynthesis breaking down carbohydrates for energy Electrolysis of water

Exothermic Reactions Exothermic Reactions: net release of energy (heat) “feels hot to the touch” ex. combustion reactions PE of Reactants > PE of Products (b/c energy is lost) Activation Energy Potential Energy (J) Time Reactants Enthalpy Products

Endothermic Reactions Endothermic Reactions: net absorption of energy (heat) “Feels cold to the touch” ex. decomposition of water using electrolysis PE of Reactants < PE of Products Activation Energy Potential Energy (J) Time Products Enthalpy Reactants

Activation Energy & Catalysts Activation energy: The amount of energy needed to get a reaction started. Required for BOTH endothermic and exothermic reactions.  

How does a catalyst speed up a reaction? Catalyst: speeds up the reaction, but is not used up during the reaction. Activated Complex Activation Energy Potential Energy (J) Time Reactants Catalyst Reduces Activation Energy Products

Enthalpy Enthalpy (ΔH): the difference in energy between the products and reactants in a chemical change ΔHreaction = Hproducts - Hreactants ΔHreaction is negative for exothermic reactions. Why? ΔHreaction is positive for endothermic reactions. Why? Nature favors lower energy  exothermic Example: 2H2 (g) + O2 (g)  2H2O (l) ΔH = -572 kJ 2H2O (l)  2H2 (g) + O2 (g) ΔH = +572 kJ

Law of Conservation of Energy Law of Conservation of Energy: the energy released when elements come together to form a compound is equal to the energy required to decompose the compound into its elements. Example: 2H2 (g) + O2 (g)  2H2O (l) ΔH = -572 kJ 2H2O (l)  2H2 (g) + O2 (g) ΔH = +572 kJ

Heating Curve Energy changes also occur in physical processes. L  G (vaporization) Gas boiling point Liquid **NOTE – Temp DOES NOT Change during a phase change!!!! BECAUSE – All the energy goes into breaking the bonds… NOT into speeding up the particles. S  L (melt) melting point Solid

Cooling Curve

Endothermic or Exothermic? Phase changes are physical changes (no new substance is formed)… Melting Freezing Boiling/Evaporation/Vaporization Condensation

Specific Heat Specific Heat (C): amount of energy (in Joules) needed to increase the temperature of 1 gram of a substance by 1oC. See Reference Tables q = mCΔT (+q = endothermic, -q = exothermic) q = heat (joules or calories) m = mass (grams) C = specific heat  ΔT = change in Temperature = Tf - Ti J goC

Remember!!! Temperature does not change during a phase change! (Energy goes into pulling molecules farther apart.) Therefore, we cannot use this equation for phase changes: q = mCΔT

Latent Heats Heat of Vaporization (Hv): amount of energy absorbed when one gram of a liquid is changed into a vapor (or, the amount of energy released when 1 gram of a vapor is changed into a liquid). q = mHv Hv = heat of vaporization (J/g) Hv of water = 2260 J/g

Heat of Fusion Heat of Fusion (Hf): amount of energy needed to convert 1 gram of a solid into a liquid. (Or the heat released when 1 gram of liquid  solid.) q = mHf Hf = heat of fusion (J/g) Hf of water = 334 J/g

Example Problems – Level One 1. How much heat is added if 100 grams of liquid water increases in temperature from 30oC to 70oC? 2. How much heat is absorbed if 200 g of ice increases in temperature from -15oC to -5oC? q = mCΔT q = (100 g)(4.18 J/goC)(70o – 30o) q = 16,720 J q = (200 g)(2.05 J/goC)(-5o – -15oC) q = 4100 J

(cont’d) 3. How much heat is released if 80 grams of water vapor is decreases in temperature from 150oC to 125oC? 4. How much heat is absorbed when 30 g of ice is changed into liquid water at 0oC? q = (80 g)(2.02 J/goC)(125o – 150o) q = - 4040 J q = mHf q = (30 g)(334 J/g) q = 10,020 J

Continued… 5. How much heat is released when 50 grams of water vapor is changed into liquid water at 100oC? q = mHv q = (50 g)(2260 J/g) q = 113,000 J  -113,000 J

Example Problems – Level Two 6. How much heat is absorbed if 30 grams of ice at -10oC is converted into liquid water? 2 steps: (1) heat the ice and (2) melt ice  liquid (1) q = mCΔT q = (30g)(2.05 J/goC)(0o – -10o) q = 615J (2) q = mHf q = (30g)(334J/g) q = 10,020J Add both steps together! Total heat = 615J + 10,020J Total heat = 10,635 J

Continued… 7. How much heat is absorbed if 45 grams of water at 80oC is converted into steam at 105oC? 3 steps: (1) heat water, (2) water  steam, (3) heat steam (1) q1 = mCΔT q1 = (45g)(4.18J/goC)(100o – 80o) q1 = 3,762 J Add all 3 together! qtotal = q1 + q2 + q3 qtotal = 3,762J + 101,700J + 454.5 J qtotal = 105,916.5 J q2 = mHv q2 = (45g)(2260J/g) q2 = 101,700 J (3) q3 = mCΔT q3 = (45g)(2.02J/goC)(105o – 100o) q3 = 454.5 J

(cont’d) 8. How much heat is released if 500 grams of vapor at 120oC changes to liquid water 70oC? 3 steps: cool the vapor, condensation, cool the liquid (1) q1 = mcpΔT q1 = (500g)(2.02J/goC)(100o – 120o) q1 = -20,200J q2 = mHv q2 = (500g)(2260J/g) q2 = 1,130,000J  - 1,130,000J Add together: -20,200J -1,130,000J + -62,700J -1,212,900J (3) q3 = mcpΔT q3 = (500g)(4.18J/goC)(70o – 100o) q3 = -62,700J

Calorimetry Calorimetry: the precise measurement of the heat flow out of a system for chemical and physical processes.

Calorimeter Example Problems 1. How much heat is released by the reaction if 10 grams of water is heated from 20oC to 60oC. q = mCΔT q = (10g)(4.18J/goC)(60o – 20o) q = 1,672J  amount absorbed by water. Therefore, -1,672J was released by the reaction. 2. What is the mass of the water if a release of 650 J of heat causes the water to increase in temperature by 15oC? (Water absorbed 650J of heat from the reaction.) 650J = m(4.18J/goC)(15oC) m = 10.4g 1. -1672 Joules (released by reaction) 2. 43 kg 3. 15 degrees Celsius

Example Problems 3. What is the final temperature of 15 g of water if the water starts at 20oC and loses 300 J of heat? **Losing heat means q is negative! -300J = (15g)(4.18J/goC)(Tf – 20o) Tf = 15.2oC 4. Determine the substance if a sample of 20 grams increases in temperature from 10oC to 28oC when it absorbs 368.3 Joules of energy. 368.3J = 20g(C)(28o – 10o) C = 4.5 J/goC  Magnesium (see ref.pack)

Entropy Entropy (S): a measure of the disorder of the particles in a system. Systems tend to become more disordered. Entropy increases when: solid  liquid  gas (melting) # moles increase in a reaction (1A + 2B  3C + 3D) Temperature increases

Predicting Changes in Entropy Predict whether ΔSsystem will be positive or negative: 1. H2O (l)  H2O (g) [positive] 2. CH3OH (s)  CH3OH (l) 3. Increase the temperature of a substance

(cont’d) 4. Dissolving of a gas in a solvent CO2 (g)  CO2 (aq) [negative] 5. What happens when the number of gaseous product particles is greater than the number of gaseous reactant particles? 2SO3 (g)  2SO2 (g) + O2 (g) [positive] 6. Generally, when a solid or liquid dissolves to form a solution? NaCl (s)  Na+ (aq) + Cl- (aq)

Spontaneous Reactions A reaction is spontaneous if: Energy decreases (energy is released = exothermic) AND Disorder increases (positive entropy). Ex. Wood burning