how are they related?. energy encountered daily is heat used or released? endothermic reactions...
TRANSCRIPT
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
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
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
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 ___________.
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
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
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?
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
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
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
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
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
Molar Heat of Vaporization Heat needed to vaporize 1 mole
of a liquid Hvap
H2O(l) H2O(g) Hvap = 40.7 kJ/mol
Molar Heat of Condensation Heat released when 1 mole of
vapor condenses Hcond
H2O(g) H2O(s) Hcond = -40.7 kJ/mol
Hvap = -Hcond
Calorimetry
Method used to determine the heat involved in a physical or chemical change.
Relies on the law of conservation of energy