Thermochemistry: 11.24
Objectives:
• Acid/Base Reaction Exam
• Thermochemistry Introduction
Thermochemistry: 11.25
Objectives:
• Acid/Base Reaction Exam-complete/modify
• Thermochemistry Introduction
Thermochemistry:
1. What is thermochemistry?
2. Determine which energy diagram is associated
with each example below:
a. Endothermic change
b. Exothermic change
c. Ice cream melting
d. Formation of snow
e. Combustion of fossil fuels: CH4 + O2 ---> H2O + CO2
f. Photosynthesis
Chem II: 12/01
Objectives:
•I can distinguish between endothermic and
exothermic processes during changes with matter.
•I can calculate and analyze energy calculations
during changes with matter.
Homework:
• Soda Can Calorimetry Pre-Lab Questions
•Calorimetry Lab: Bring junk food/aluminum can
(12oz.)
Thermochemistry:
1. What is thermochemistry?
2. Determine which energy diagram is associated
with each example below:
a. Endothermic change
b. Exothermic change
c. Ice cream melting (endo)
d. Formation of snow (exo)
e.
Combustion of fossil fuels: CH4 + O2 ---> H2O + CO2 (exo)
f. Photosynthesis (endo)
Energy Diagrams
Primary Phase Changes
Sublimation
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Deposition
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Thermochemistry
• Study of energy changes between matter during a
physical or chemical change.
• What are the two states of energy?
Thermochemistry
• Study of energy changes between matter during a
physical or chemical change.
• What are the two states of energy?
-Potential Energy= stored energy, energy in chemical
bonds
-Kinetic Energy = energy of motion; particle movement
during physical or chemical changes.
• Primary forms of energy in chemistry:
*chemical, thermal, visible light, and electrical
Heat Energy
Heat Energy:
• Energy that is transferred between matter of
different temperatures.
• Kinetic Energy-movement between matter.
• Heat Energy Units: Joules (J) or calories (cal)
• Energy does not have mass or volume, therefore it
is NOT classified as matter.
• How does heat energy flow between objects of
different temperatures?
Heat Energy Flow
Energy flows between:
• The System:
The matter you are studying/measuring.
• The Surrounding :
The matter (environment) around the system.
Energy Processes:
• Endothermic Process:
When more heat is absorbed by the system.
• Exothermic Process:
When more heat is released by the system.
Energy Diagrams
Conservation of Matter and Energy
Matter:
•Matter undergoes
changes, but the atoms are
conserved.
Energy:
•Energy is also conserved during
changes.
•If energy increases for a system,
then its surroundings must
decrease in energy by the same
amount.
•1st Law of Thermodynamics
Energy Changes: Thermometer
•Energy changes between the system and its
surroundings can be measured using a thermometer.
•(Energy changes = Temperature changes)
•Temp. change indicates a change in speed of
particles of system or surroundings.
•Primary unit of measurement by scientists:
Celsius (oC) and Kelvin (K) scales
Thermometers
Visionlearning.com
K = oC + 273
Thermochemistry
What factors do you think influence energy transfer
between objects?
Thermochemistry
What factors do you think influence energy transfer
between objects?
- chemical make-up of the matter
- the mass of the matter
- temperature difference between the matter
Specific Heats of Common Substances
Substances
Specific Heat
J/g* 0C
Specific Heat
cal/g*oC
water
4.18
1.00
Grain alcohol
2.4
0.58
ice
2.1
0.50
steam
1.7
.40
aluminum
0.90
0.21
silver
0.24
0.057
mercury
0.14
0.033
Energy Equation
Chem II: 12/02
Objectives:
•I can distinguish between endothermic and
exothermic processes during changes with matter.
•I can calculate and analyze energy calculations
during changes with matter.
Specific Heat Calculations
• The temperature of a 95.4 gram piece of copper
increases from 25.0oC to 48.0oC when the copper
absorbs 849 Joules of heat. What is the specific heat of
copper?
Chem II: 12/03
Objectives:
•I can distinguish between endothermic and
exothermic processes during changes with matter.
•I can calculate and analyze energy calculations
during changes with matter.
Soda Can Calorimetry Lab
Purpose:
To indirectly determine the Calorie content in
specific snack foods.
Pre-Lab:
• Read background and complete pre-lab questions.
Soda Can Calorimetry Lab
Purpose:
To indirectly determine the Calorie content in specific
snack foods.
Pre-Lab:
• Read background and complete pre-lab questions.
Homework:
• Complete pre-lab qts. and bring in junk food and a
12oz. soda can.
Chem II: 12/04
Objectives:
•I can calculate and analyze energy calculations
during changes with matter.
*Analyze data and establish conclusion for the Soda
Can Calorimetry Lab
*Receive Final Exam Study Guide
Chem II: 12/05
Objectives:
•I can calculate and analyze energy calculations
during changes with matter.
*Experimental analysis and calculation of energy data
(Soda Can Calorimetry)
*Theoretical analysis and calculation of energy data
(Thermochemical Equations)
Experimental Analysis: Soda Can Calorimetry
Q=mc T
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Calorimetry
• Measurement of
heat flow in and out
of a system during
physical/chemical
changes.
• Energy equation and
1st Law of Thermodynamics
is used to calculate energy
transferrred by system.
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Enthalpy
• The amount of energy released or absorbed by a system.
• Enthalpy symbol (H)
• Enthalpy (H) = Heat Energy (Q) if pressure is constant.
•
H=
Thermochemical Equations
• A chemical equation that includes the enthalpy
change of a reaction at constant pressure.
1. CaO (s) + H2O(l) -----> Ca(OH)2 (s) + 65.2 kJ
CaO (s) + H2O(l) -----> Ca(OH)2 (s)
H = -65.2 kJ
2. 2Na(HCO3)(s) + 129kJ -----> Na2(CO3) (s) + H2O (l) + CO2 (g)
2Na(HCO3) (s) -----> Na2(CO3) (s) + H2O (l) + CO2 (g)
H= 129 kJ
H = heat of reaction
Thermochemical Equation: Standard Conditions
CaO (s) + H2O(l) -----> Ca(OH)2 (s)
H = -65.2 kJ
Standard Conditions :
• Standard temperature , 25oC (room temp.)
• Standard pressure, 1atm.
• Reactants/products states of matter at room temp.
• Chemical equation is balanced.
• Establish a relationship between enthalpy changes
and moles of substances in balanced equations.
Thermochemical Equation Applications
Using the thermochemical equation below, calculate
the amount of heat in kJ required to decompose
2.24 mol Na(HCO3).
• 2Na(HCO3) (s) -----> Na2(CO3) (s) + H2O (l) + CO2 (g)
H= 129 kJ
Heats of Reaction Calculations
Chem II: 12/09
Due:
• Soda Can Calorimetry Lab Report
• Heats of Reaction Problems
Objectives:
•I can calculate and analyze energy calculations
during changes with matter.
*Experimental calculation and analysis of energy data
(Soda Can Calorimetry)
*Theoretical calculation and analysis of energy data.
(Thermochemical Equations)
Thermochemistry Bell Ringer
1. a. What is enthalpy?
b. What are two ways in which scientists can
determine the enthalpy of a system?
2a. Give an example of a thermochemical equation.
b. Explain how you know if it is endo. or exo.
c. Identify standard conditions for a
thermochemical equation.
Soda Can Calorimetry Lab
Q=mc T
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Heats of Reaction Problems
Heat of Combustion
• Heat of reaction for the complete burning of one
mole of fuel.
CH4 (g) + 2O2 (g) -----> H2O(l) + CO2 (g)
H = -890kJ
Substance
Chemical Formula
Enthalpy Change
(kJ/mol)
Hydrogen
H2
-286
Carbon
C (s) graphite
-394
Methane
CH4 (g)
-890
Ethanol
C2H5OH
-1,368
Enthalpy: Changes in State
• Molar heat of fusion
• Molar heat of solidification
• Molar heat of vaporization
• Molar heat of condensation
Enthalpy: Changes in State
• Molar heat of fusion: H(fus)
Amount of heat absorbed by one mole of solid as it melts to
a liquid at constant temperature.
• Molar heat of solidification: H(solid)
Amount of heat released by one mole of liquid as it freezes
to a solid at constant temperature.
• Molar heat of vaporization: H(vap)
Amount of heat absorbed by one mole of liquid as it
vaporizes to a gas at constant temperature.
• Molar heat of condensation: H(cond)
Amount of heat released by one mole of gas as it condenses
to a liquid at constant temperature.
Heat Curve Graph
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Enthalpy: Heat of Solution
Molar Heat of Solution: H(soln.)
• Heat is either absorbed or released during the
formation of a solution.
• The enthalpy change caused by the dissolution of
one mole substance.
• Ex. Na(OH) (s) -----> Na+(aq) + OH- (aq)
H(soln.) = -445.1kJ/mol
Energy Calculations: Homework
Homework Problems: (pg. 535-536)
*43., 46., 47., 55., 56., 58., 59., 62., 66., 69.
*Energy conversions: 1,000cal = 1Cal
1 J = 0.2390 cal
Classroom Problems
Calculating Heats of Reaction (pg. 527)
1. Why would scientists need to calculate the heats
of reaction, H, when they can measure it by
performing the reaction in the lab?
2. What are ways scientists can calculate heats of
reaction without performing the reaction in the
lab.
Calculating Heats of Reaction (pg. 527)
1. Why would scientists need to calculate the heats
of reaction, H, when they can measure it by
performing the reaction in the lab?
• Reaction might occur too slowly to measure.
• Reaction might be an intermediate step in a
multi-step reaction.
• Might want to preserve reactants in a reaction.
• Reaction in lab might yield side products
(unwanted products) that affects the H.
Heat of Reaction Calculations
• Enthalpy change can be calculated two ways:
* Hess’s Law: Sum of several thermochemical
equations.
*Standard Heat of Formation: The difference in heat
of formation of products and reactants in the
reaction.
H = Hf (products) - Hf (reactants)
Hess’s Law: Sum of Reactions
CH4(g) + 2O2 (g) ----> CO2 (g) + 2H2O(l)
H =?
C(s) + 2H2 (g) -----> CH4(g)
H = -74.80 kJ/mol
C(s) + O2 (g) -----> CO2 (g) H = -393.50 kJ/mol
H2 (g) + 1/2O2 (g)----> H2O (l) H= -285.83 kJ/mol
Chem II: 12/10
Due:
• Soda Can Calorimetry Lab Report
• Heats of Reaction Problems
Objectives:
•I can calculate and analyze energy calculations
during changes with matter.
*Experimental calculation and analysis of energy data
(Soda Can Calorimetry)
*Theoretical calculation and analysis of energy data.
(Thermochemical Equations)
Calorimetry Lab: Class Data
Lab Group
Food Burned and
Energy/Gram (Cal/g)
% Error
Hess’s Law: Sum of Reactions
CH4(g) + 2O2 (g) ----> CO2 (g) + 2H2O(l)
H =?
C(s) + 2H2 (g) -----> CH4(g)
H = -74.80 kJ/mol
C(s) + O2 (g) -----> CO2 (g) H = -393.50 kJ/mol
H2 (g) + 1/2O2 (g)----> H2O (l) H= -285.83 kJ/mol
Chem II: 12/11
Due:
• Hess’s Law Problems (qts.6-8)
Objectives:
•I can calculate and analyze energy calculations
during changes with matter.
(Hess’s Law and Heat of Formation)
Homework:
• Soda Can Calorimetry Lab –Formal Report due Fri.
• Enthalpy Calculation Problems
Hess’s Law Calculations
Standard Heat’s of Formation
CH4(g) + 2O2 (g) ----> CO2 (g) + 2H2O(l)
H =?
• Can calculate using standard heats of formation if
occurs at standard conditions.
H = Hf (products) - Hf (reactants)
• Standard Heats of Formation table (pg. 530)
CH4(g) H =
O2 (g) H =
CO2(g) H =
H2O(l) H =
Chem II: 12/12
Due:
• Soda Can Calorimetry-formal lab report
• Hess’s Law Problems (qts.66-74)
Objectives:
•I can calculate and analyze energy calculations
during changes with matter.
(Hess’s Law and Heat of Formation)
Homework:
• Chemistry Final Review
Hess’s Law
Hess’s Law: Exit Slip
2H2(g) + 2C(s) + H2O(g) ---> C2H5OH(l)
C2H5OH + 3O2 ----> 2CO2 (g) + 3H2O
Standard’s Heat of Formation
Homework Problems
Homework Problems: (pg. 535-536)
*43., 46., 47., 55., 56., 58., 59., 66., 69.
In addition: 67., 69., 72., 73., 74., 82
Gallery Walk Practice Problems
• Apply Hess’s Law and Standard Heats of
Formation in calculating heats of reaction.
Energy Calculations: Homework
Homework Problems: (pg. 535-536)
*43., 46., 47., 55., 56., 58., 59., 66., 69.
*Energy conversions: 1,000cal = 1Cal
1 J = 0.2390 cal
In addition: 67., 69., 72., 73., 74., 82
Calculating Heats of Reaction