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What is an endothermic reaction?
A chemical reaction that absorbs heat from its surroundings.
In an endothermic reaction, which has more energy: the products or the reactants.
The products have more energy than the reactants.
What is an exothermic reaction?
A chemical reaction that releases heat into its surroundings.
In an exothermic reaction, how does the energy of the products compare to the reactants?
Products have less energy than the reactants.
Thermodynamics.
The study of energy transfer and energy changes.
Thermochemistry.
The study of heat energy which is associated with chemical reactions and/or physical transformations: a reaction may release or absorb energy.
First Law of Thermodynamics.
The total energy in the universe is constant. Universe = system + surroundings.
Second Law of Thermodynamics
When two objects are in thermal contact and are at different temperatures, the thermal energy must be transferred from the system at a higher temperature to the one at a lower temperature so that the system becomes disorderly.
Disorderly
The particles having different kinetic energies are completely mixed.
Open system
Both matter and energy are allowed to enter and leave the system.
Closed system
Energy can enter or leave the system but matter cannot.
Isolated system
Neither energy nor matter are allowed to enter or leave the system.
What are sources of energy from the environment converted to?
Electricity, heat, mechanical energy, light, and sound.
What are fossil fuels used for?
Heating (15%)
Transportation (30%)
Industry (40%)
Commercial/Institutional (15%)
Calorimetry
A technological process measuring energy changes in an isolated system.
Temperature and Kinetic Energy
An increase in temperature causes an increase in the kinetic energy of the particles and the vice versa.
What do you need to know in order to calculate the amount of heat that has entered a substance (or left a substance)?
Temperature changes of the substances, quantity of the substance, and heat capacity of the substance.
Q=mc(delta)t
Q = thermal energy (in joules) or KJ
m = mass of substance (g) or kg
c = specific heat capacity (J/g°C)
t = change in temperature of the substance (°C)
Calorimetry
The measure of energy change in an isolated system.
What assumptions do you need for calculations in enthalpy/calorimetry?
The calorimeter detects all changes, system is isolated, specific heat capacity of water (4.19J/g°C), the specific heat capacity of a dilute solution is the same as water, the density of a solution is the same as water, the energy gained/lost by the container is negligible.
Enthalpy
The total (sum) of all kinetic and potential energy of a system under constant pressure.
Enthalpy change (🔺H)
When a system under constant pressure changes.
What are the two fundamental types of energy?
Kinetic and potential.
Enthalpy change (🔺H) is equal to what during chemical reactions?
The heat, Q (thermal energy), absorbed or released by the system.
Kinetic Energy (Ek)
The energy of motion of particles. A change in temperature (🔺t) signals a change in kinetic energy.
Potential Energy (Ep)
Energy that is stored in chemical bonds. This energy is usually gained/lost during chemical reactions (breaking or forming of intramolecular bonds).
Intramolecular
Interactions or forces that occur within a single molecule.
Calorimetry
The total energy in a chemical system is equal to the total energy change of a calorimeter.
🔺rHm (KJ/mol)
🔺 - change
r - reaction (can vary)
H - enthalpy
m - moles
What is the enthalpy change per chemical amount (mol)?
Molar enthalpy of a reaction - 🔺rHm KJ/mol.
Molar Enthaply
The enthalpy of a reaction equals the chemical amount of a substance multiplied by the molar enthalpy of the reaction.
🔺H
Endothermic
-🔺H
Exothermic
n🔺cHm = mc🔺t
n - chemical amount of fuel
🔺cHm - molar enthalpy of combustion of fuel
m - mass of water
c - specific heat capacity of water
🔺t - temperature change of water
4 methods of communicating energy changes
Molar enthalpy.
As a term at the end of the reaction.
As a term within a balanced equation.
On a potential energy diagram.
Communicating energy changes: 🔺H is positive
(Endothermic) put the energy as a reactant
Communicating energy: -🔺H
(Exothermic) put the energy as a product.
