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AP Chemistry ~ Thermodynamics

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Section 1

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ΔH(rxn)

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Chemistry Science

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Mar 1, 2020

Cards (41)

Section 1

(41 cards)

ΔH(rxn)

Front

The heat lost or gained in the balanced chemical equation (ratio)

Back

Formula: Change in System's Energy

Front

ΔE = q + w ΔE - Change in PE and KE of system q - Heat transferred in J w - work done on system by surroundings (endo)/work done on surroundings by system (exo)

Back

ΔG(f)

Front

Free energy change that occurs when one mole of a compound is made from its elements in their standard states = 0 when element is in standard state

Back

Enthalpy of Formation

Front

A hypothetical value that indicates how much heat would be lost or gained during the formation of one mole of a compound ΔH(f) value for any element in elemental state is 0

Back

Gibbs Free Energy

Front

The maximum amount of energy that can be used to do work If ΔG is negative, the reaction is TFP

Back

Temperature and Thermodynamic Favorability

Front

Back

2nd Law of Thermodynamics

Front

The entropy of the universe is constantly increasing Slowly expanding and becoming more disorderly

Back

Formula: ΔH(rxn) with Formation

Front

ΔH(rxn) = ΣnH(products) - ΣnH(reactants) Under standard conditions, the total change in enthalpy is equal to the sum of coefficients times formation values for products, minus the sum of coefficients times formation values for reactants

Back

Thermodynamically Favored Process

Front

Happens without any assistance from surroundings Ex: Water evaporates at 25 C, Iron rusts with O2 and H2O, NaCl dissolves in water Likely to happen!

Back

Formula: ΔS Universe

Front

ΔS(universe) = ΔS(system) + ΔS(surroundings) If ΔS(universe) is positive, the rxn is TFP

Back

Non-Thermodynamically Favored Process

Front

Assistance from the surroundings is necessary to induce the desired change Ex: heat up, cool down, etc. Change amount of energy

Back

Examples: ΔS>0

Front

- Melting - Vaporization - Reactants contain less particles than products - Dissolving - Adding heat - Increasing volume of gas - solid to liquid - liquid to gas

Back

Formula: Heat Lost/Gained with c

Front

q = mcΔT Heat lost or gained (J) is the mass, times the specific heat, times the change in temperature

Back

Bond Enthalpy

Front

The energy needed to break or create a bond Formation - energy released (exothermic) Break - energy added (endothermic)

Back

Formula: ΔH with Bond Enthalpy

Front

ΔH = ΣBE(bonds broken) - ΣBE(bonds formed) Hint: B comes before F alphabetically, so Broken comes before Formed Exothermic process - more bonds formed (-ΔH) Endothermic - more bonds broken (+ΔH)

Back

ΔG>0

Front

External energy can drive reactions to make them occur Non-TFP Ex: electricity to charge battery, photosynthesis

Back

System

Front

The actual chemical reaction that is taking place

Back

Calorimeter

Front

A device used to determine the amount of heat transferred

Back

Temperature

Front

A measure of the average kinetic energy of atoms and molecules in a system. Kelvin (K) is directly proportional to kinetic energy

Back

Enthalpy

Front

The heat that is released or absorved in a chemical reaction

Back

q(rxn)

Front

The heat lost or gained in the experiment that took place in the calorimeter (numeric value)

Back

Hess's Law

Front

The overall enthalpy change of a rxn will be the same if it is carried out in one step or in several steps ΔH(1) + ΔH(2) = ΔH(3) where ΔH(1) & ΔH(2) are steps of ΔH(3)

Back

Formula: Gibbs Free Energy

Front

ΔG = ΔH - TΔS The free energy change in kJ is the enthalpy change in kJ minus the temperature of the system in K times the entropy change in kJ/K

Back

Boltzmann Distribution

Front

The distribution of kinetic energies increases as temperature increases The average KE of the particles in a system increases as temp increases

Back

Formula: Gibbs Free Energy with Formation

Front

ΔG(rxn) = ΣnΔGf(products) - ΣnΔGf(reactants) The Change in free energy is the sum of coefficients times the formation values of produces minus the sum of coefficients times formation values of reactants

Back

Thermodynamics

Front

The relationship between chemical reactions and heat Concepts: Enthalpy, Entropy, Free Energy

Back

Entropy (S)

Front

A measure of the disorder of a system Positive value for ΔS is favorable

Back

Specific Heat Capacity

Front

(c) The amount of heat required to raise 1 g of a substance by 1 K

Back

Exothermic Process

Front

Heat EXITS the system into the surroundings High potential energy --> High Kinetic energy Often thermodynamically favored

Back

Bond Energy

Front

The further apart the atoms in a bond, the greater the bond energy

Back

Calorimetry

Front

The measurement of heat transfer

Back

Surroundings

Front

The entire universe outside of the chemical reaction. Remember: For solutions (aqueous reactions), the water is a part of the surroundings!

Back

Formula: Entropy

Front

ΔS = ΣnS(products) - ΣnS(reactants) Universe favors greater disorder (+ΔS)

Back

Isolated System

Front

Energy is conserved

Back

Heat

Front

A form of energy measured in Joules (J)

Back

Formula: Enthalpy

Front

ΔH = H(products) - H(reactants) Calculates the overall change in heat (heat absorbed or released in the reaction) by finding the final heat contained within the produces minus the initial heat contained within the reactants Hint: Enthalpy has an H so it is ΔH

Back

Endothermic Process

Front

Heat flows INTO the system from the surroundings High kinetic energy --> High potential energy Creates disorder

Back

Gibbs Free Energy

Front

The maximum amount of energy that can be used to do work If ΔG is negative, the reaction is TFP

Back

Formula: Transfer of Energy Through Work

Front

w = -PΔV Associated with changes in the volume of a gas. Negative work - gas expands Positive work - gas contracts

Back

Law of Conservation of Energy

Front

Energy can be neither created nor destroyed, but it can be transformed from one form to another.

Back

1st Law of Thermodynamics

Front

The energy contained within the universe is constant

Back