chemistry and energy
DESCRIPTION
How are they related?. Chemistry and Energy. Energy Encountered Daily. Is Heat Used or Released?. Endothermic reactions used heat from the surroundings Sweating Refrigeration Exothermic heat releases heat to the surroundings Hot hands Combustion Exercise. Endothermic Reactions. - PowerPoint PPT PresentationTRANSCRIPT
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How are they related?
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Energy Encountered Daily
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Is Heat Used or Released? Endothermic reactions used heat
from the surroundings Sweating Refrigeration
Exothermic heat releases heat to the surroundings Hot hands Combustion Exercise
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Endothermic Reactions
Decrease in kinetic energy decrease in temperature heat will transfer from the environment to the system resulting in a cooler environment
Absorbs heat from its surrounding. The system gains heat Positive value for q H = q = 0 Hproducts Hreactants
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Exothermic Reactions
Increase in kinetic energy increase in temperature of system heat released to the environment resulting in a hotter environment
Releases heat to its surroundings The system loses heat Negative value for q H = q = 0 Hproducts Hreactants
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Enthalpy
Heat content for systems at constant pressure
Symbol is H Terms heat and enthalpy are used
interchangeably for this course H = q = m C T
Heat moves from ________ to ___________.
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Law of Conservation of Energy
Energy is not lost or gained in a chemical reaction
In a chemical reaction potential energy is transferred to kinetic energy
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Thermochemical Equations
An equation that includes the heat change
Example: write the thermochemical equation for this reaction CaO(s) + H2O(l) Ca(OH)2(s) H = -
65.2 kJ
CaO(s) + H2O(l) Ca(OH)2(s) + 65.2 kJ
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Stoichiometry and Thermochemistry
Tin metal can be extracted from its oxide according to the following reaction:
SnO2(s) + 4NO2(g) + 2H2O(l) + 192 kJ Sn(s) + 4HNO3(aq)
How much energy will be required to extract 59.5 grams of tin?
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How to solve
1. Use your stoichiometry2. Treat heat as a reactant or
productSnO2(s) + 4NO2(g) + 2H2O(l) +
192 kJ Sn(s) + 4HNO3(aq)59.5 g Sn 1 mol Sn 192 kJ 1 g Sn 1 mol Sn
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If an Object feels hot, it means it is undergoing a change with a H that is:
a. positiveb. negativec. whether the object feels hot
or not is unrelated to its Hd. I don’t know
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If the object feels hot, it means it is undergoing:
a. an exothermic reactionb. an endothermic reactionc. whether it feels hot or not is
unrelated to whether it is undergoing an exothermic or an endothermic change
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How does ice melt?
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Molar Heat of Fusion
Heat absorbed by one mole of a substance during melting
Constant temperature Hfus H2O(s) H2O(l) H = 6.01
kJ/mol
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Molar Heat of Solidification Heat lost when 1 mole of a liquid
solidifies Temperature is constant Hsolid Hfus = -Hsolid
H2O(l) H2O(s) H = -6.01 kJ/mol
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Molar Heat of Vaporization Heat needed to vaporize 1 mole
of a liquid Hvap H2O(l) H2O(g) Hvap = 40.7
kJ/mol
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Molar Heat of Condensation Heat released when 1 mole of
vapor condenses Hcond
H2O(g) H2O(s) Hcond = -40.7 kJ/mol
Hvap = -Hcond
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Phase Change Diagram for Water
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Phase Change Diagram
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The House that Heats Itself http://www.sciencefriday.com/videos/
watch/10007
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Calorimetry
Method used to determine the heat involved in a physical or chemical change.
Relies on the law of conservation of energy
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Calorimeter
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Simple Calorimeter
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Calorimetry Math Heat gained by the water = q Heat lost by the system = -q
mCT = q T = Tf –Ti , m = mass, C = specific heat
q gained by water = q lost by system q water = - q system mCT = -mCT(mass H2O)(spec. heat H2O)(T H2O) = -
(mass sys)(spec. heat sys)(T sys)