Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf ·...
Transcript of Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf ·...
![Page 1: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/1.jpg)
Thermochemistry is the study of heat change in chemical
reactions.
Chapter 5
Energy & Rates of Reaction
Unit 3
![Page 2: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/2.jpg)
Chapter 5 Key Concepts: After completing this chapter you will be able to…..
• Compare the energy changes of different substances, perform calorimetry calculations, and describe the relationship between reactions using enthalpy terms.
• represent thermochemical equations using different methods, and determine whether a reaction is exothermic or endothermic
• Calculate and use bond energies to estimate the enthalpy change of a reaction.
• Define and solve problems using Hess’s law.
• Write formation reactions and calculate enthalpy changes using standard enthalpy of formation values.
• Describe current and future energy sources and explain their advantages and disadvantages
![Page 3: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/3.jpg)
Energy: is the capacity to do work (units Joules, J)
• Work transferred energy by a force causing an object to move a distance (unit Joules)
• Thermal energy is the total quantity of potential and kinetic energy within a substance.
• Potential energy is the energy available due to an object’s position or composition
• Kinetic energy is the energy of the object in motion.
5.1
![Page 4: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/4.jpg)
Heat is the transfer of thermal energy between two bodies that are at different temperatures. Heat moves from warm objects to cooler objects
Energy Changes in Chemical Reactions
Temperature is a measure of the average kinetic energy of the particles in a substance.
Temperature = Thermal Energy
900C 400C
greater thermal energy 5.1
![Page 5: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/5.jpg)
Law of Conservation of Energy:
Energy cannot be created or destroyed
The system is the specific part of the universe that is of interest in the study.
open
mass & energy Exchange:
closed
energy isolated nothing
SYSTEM
SURROUNDINGS
5.1
![Page 6: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/6.jpg)
Exothermic process is any process that gives off heat – transfers thermal energy from the system to the surroundings.
Endothermic process is any process in which heat has to be supplied to the system from the surroundings.
2H2 (g) + O2 (g) 2H2O (l) + energy
H2O (g) H2O (l) + energy
energy + 2HgO (s) 2Hg (l) + O2 (g)
5.1
energy + H2O (s) H2O (l)
![Page 7: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/7.jpg)
Nuclear Energy
• All nuclear reactions are exothermic. • Nuclear reactions release much more energy than exothermic
chemical reactions – per unit of mass. • Two main types of Reactions: Fusion and Fission • A fusion reaction occurs when two or more nuclei of small atomic
mass combine to form larger molecule. 21H + 31H → 42He + 10n
In Fission, large nuclei with high atomic mass are split to smaller,
lighter mass by collision with a neutron:
23592U + 10n → 92
36Kr + 14156Ba + 31
0n + 1.9 x 10 10 kJ/mol 5.1
![Page 8: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/8.jpg)
The specific heat (c) of a substance is the amount of heat (q) required to raise the temperature of one gram of the substance by one degree Celsius.
5.2: Calorimetry and Enthalpy
The heat capacity (C) of a substance is the amount of heat (q) required to raise the temperature of a given quantity (m) of the substance by one degree Celsius.
C = mc Heat (q) absorbed or released:
q = mcΔT
q = CΔT
ΔT = Tfinal - Tinitial
5.2
![Page 9: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/9.jpg)
Calorimetry: the measurement of heat into or out of a system for chemical and physical processes.
the heat released = the heat absorbed The device used to measure the absorption or release of heat in chemical or physical processes is called a “Calorimeter”
5.2
![Page 10: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/10.jpg)
a “Calorimeter”
![Page 11: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/11.jpg)
Calorimetry Calculations When analyzing data obtained using a calorimeter, make these assumptions:
• Any thermal energy transferred from the calorimeter to the outside environment is negligible.
• Any thermal energy absorbed by the calorimeter itself is negligible.
• All dilute, aqueous solutions have the same density (1.00 g/mL) and specific heat capacity (4.18 J/(g·°C)) as water
• Thermal energy absorbed or released by a chemical system is given the symbol q .
qwater = mcΔT
5.2
![Page 12: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/12.jpg)
Calculations Involving Thermal Energy Transfer Thermal Energy transfer by metal
No heat enters or leaves! 5.2
How much heat is given off when an 869 g iron bar cools from 940C to 50C? Solution: Given: c of Fe = 0.444 J/g • 0C m = 869 g ΔT = Tfinal – Tinitial = 50C – 940C = -890C q = mcΔt = 869 g x 0.444 J/g • 0C x (–890C) = -34,000 J
![Page 13: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/13.jpg)
5.2
A student places 50.0 mL of liquid water at 21.00 °C into a coffee-cup calorimeter. She places a sample of gold at 100 °C into the calorimeter. The final temperature of the water is 21.33 °C. The specific heat capacity of water is 4.18 J/g·°C and the density of water, d, is 1.00 g/mL. Calculate the quantity of thermal energy, q , absorbed by the water in the calorimeter
Calculations of metal in water
![Page 14: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/14.jpg)
SOLUTION: Given: VH2O = 50.0 mL; c = 4.18 J/(g·°C) dH2O = 1.00 g/mL; Tinitial=21.00 °C; Tfinal=21.33 °C Unknown q = ? Equations d =m/v m=vd ∆T = Tfinal – Tinitial
1. Determine Mass m= vd, m =50mL x 1.00g/mL = 50 g 2. Determine Temperature change ∆T = 21.33oC – 21.00oC Calculate Themal energy q = mc∆t =50 g x 4.18 J x 0.33oC g. oC = 69 J The thermal energy absorbed by the water is 69 J.
![Page 15: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/15.jpg)
Determining specific heat capacity of a substance Using the value of q above, calculate the specific heat capacity, c, of gold if its mass is 6.77 g. Final temperature of the gold is same as that of water in the calorimeter.
![Page 16: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/16.jpg)
Given: mAu =6.77 g q = 69 J (+ or - ?) T initial =100 oC T final = 21.33oC ∆T =21.33 oC – 100oC = - 78.67 oC Required: cAu q = mc∆T Rearrage and solve for c
c = q/m∆T c = (-69J)/(6.77g x -78.67oC) c = 0.13 J/g oC The specific heat capacity of the sample of gold is 0.13 J/g oC
![Page 17: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/17.jpg)
Enthalpy (H): Total amount of thermal energy in a substance
Enthalpy Change (∆H) :
Energy changes in Physical and Chemical Reactions The enthalpy change of the chemical system is equal to the flow of thermal energy in and out of the system,
∆H system = |q system| ∆H > 0 Endothermic reaction ∆H < 0 Exothermic reaction
5.2
![Page 18: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/18.jpg)
ΔH = H (products) – H (reactants) ΔH = heat given off or absorbed during a reaction at constant pressure
Hproducts < Hreactants
ΔH < 0
Hproducts > Hreactants
ΔH > 0 5.2
Energy Changes during Exothermic & Endothermic Reaction in an Open System
![Page 19: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/19.jpg)
Molar Enthalphy Change
Energy changes involving 1 mole of a substances… (∆H) ∆H = n∆Hr
Where n is the amount and ∆Hr is the molar enthalpy change of the reaction Types of Molar Enthalpies of Reaction Solution (∆Hsol) NaBr(s) →Na(aq) + Br(aq)
Combustion (∆Hc) CH4(g) + 2O2(aq) → CO2(aq) + H2O(l)
Vapourization (∆Hvap) CH3OH(l) → CH3OH(g)
Neutralization (∆Hneut) 2NaOH(aq) + H2SO4(aq) →Na2SO4(aq) + H2O(l)
Formation (∆Hf) C(s) +2H2(g) + 1/2O2(g) → CH3OH(l)
5.2
![Page 20: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/20.jpg)
Molar Enthalpy Calculations
Given: methanol=1.00 g; ∆Hvap=38.6 kJ/mol ∆H = ? n = ? Equation: ∆H = n∆Hvap
5.2
Methanol= 24 +6 +16 = 46g/mol
n = m / M n = 1 g x 1 mol/46 g = 0.022 ∆H = 0.022 mol x 38kJ/mol = 0.836 KJ = 836 J
Calculate ∆H for Vaporization Reactions Ethanol, CH3CH2OH(l), is used to disinfect the skin prior to an injection. If a 1.00 g sample of ethanol is spread across the skin and evaporated, what is the expected enthalpy change? The molar enthalpy of vaporization of ethanol is 38.6 kJ/mol.
![Page 21: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/21.jpg)
Representing Molar Enthalpy Changes
Energy changes can be communicated in four different ways. Three of them are thermochemical equations and one uses diagram. 1. By including an energy value as a term in the thermochemical equation e.g., CH3OH(l) + 3/2 O2 → CO2(g) + 2H2O(g) + 726 KJ(Exothermic Reaction) 2. By writing a chemical equation and stating its enthalpy change e.g., CH3OH(l) + 3/2O2(g)→CO2(g)+ 2H2O(g) ∆H = -726 KJ (Exothermic
Reaction)
3. By stating the molar enthalpy of a specific reaction e.g., ∆Hcombustion or ∆Hc = - 726 KJ/mol CH3OH
![Page 22: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/22.jpg)
4. By drawing a chemical potential energy diagram Note: Fractions are convenient in many thermochemical equations. They apply to fractions of moles of substances e.g., 3/2 mol represents 1.5 mol rather than fractions of actual molecules
5.2
![Page 23: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/23.jpg)
H2O (s) H2O (l) ΔH = 6.01 kJ
Is ΔH negative or positive?
System absorbs heat
Endothermic
ΔH > 0 6.01 kJ are absorbed for every 1 mole of ice that melts at 00C and 1 atm.
5.2
Potential Energy Diagram
Thermochemical Equations
![Page 24: Energy & Rates of Reactionmrlittles.weebly.com/uploads/1/0/4/3/10438176/thermochemistry.pdf · calorimetry calculations, and describe the relationship between reactions using enthalpy](https://reader030.fdocuments.in/reader030/viewer/2022040203/5e8b1e77aaf7ee1f963654a2/html5/thumbnails/24.jpg)
CH4 (g) + 2O2 (g) CO2 (g) + 2H2O (l) ΔH = -890.4 kJ
Is ΔH negative or positive?
System gives off heat
Exothermic
ΔH < 0
890.4 kJ are released for every 1 mole of methane that is combusted at 250C and 1 atm.
5.2
Thermochemical Equations