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Chapter 6
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= the capacity to do work or to produce heat Kinetic energy = the energy due to motion depends on mass & velocity Potential Energy = energy due to the position or composition.
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Temperature = reflects the random motions of particles in a substance. The more motion the higher the temperature. Heat = Involves the transfer of energy between two objects due to a temperature difference.
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The portions of universe that is identified Two Types: Open system: the designated part is open to the atmosphere. Closed system: the designated part is closed to the atmosphere.
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2 ways 1. work = force x distance 2. heat
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A property that is related only to the current conditions—There is no consideration as to how it got to the current situation. Examples: pressure, volume, temperature, energy and enthalpy
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System-reactants and products Surrounding-everything else
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Also known as the Law of Conservation of Energy Energy cannot be created nor destroyed but may be conserved. Concept describes the universe not a system.
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Thus, energy can be lost or gained by a system. Energy in the universe is constant. Thermodynamics = the study of energy and its conversions
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= sum of the kinetic and potential energies of all “particles” in the system. ΔE = q + w q = heat W = work
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Consists of two parts: a. Number = gives the magnitude of the change b. sign 1. (+) = endothermic 2. (-) = exothermic
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The energy is exchanged with the environment in terms of heat or work. ΔE = q + w q = (+) means that heat is added to the system q = (-) means that heat is subtracted from the system
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Negative work = energy flows out of the system so the system does work on the surroundings --exothermic Positive work = energy flows into the system so the surrounding do work on the system --endothermic When the systems are under relatively standard conditions the effects of work is ignored.
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ΔH = ΔE + PΔV ΔE = change in internal energy P = pressure of the system ΔV = change in volume of the system ΔH = is equal to the energy flow as
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ΔH = ΔH products – ΔH reactants -ΔH = exothermic +ΔH = endothermic
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Loss or gain of heat by a system is enthalpy. (ΔH) State Function ΔH = H f – H i = q p q p is heat associated with constant pressure
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Positive value of ΔH means that the system has gained heat from the surrounding. (endo) Negative value of ΔH means that the system has lost heat to the surroundings. (exo)
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Heat Capacity is the amount of heat required to raise the temperature of a substance 1°C. Molar Heat Capacity is the heat capacity of one mole of the substance. Specific Heat Capacity is the heat capacity of gram values of a substance. The specific heat of a substance is the amount of heat required to raise 1 gram of the substance 1°C.
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q = m x c x ΔT q = heat M = mass in grams c = specific heat in J/g°C ΔT is the difference between final and initial temperature in°C
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A 2.50 kg piece of copper metal is heated from 25°C to 225°C. How much heat kJ, is absorbed by the copper. The specific heat is 0.384 J/g°C for copper. q = 192 kJ
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The enthalpy of a reaction is equal to the sum of the enthalpies for each step. Allows us to calculate the enthalpy of the reaction by using information about each reactant.
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ΔH° Enthalpy for a reaction when all reactants and products are in their standard state. Standard state is 25°C and 1 atm ΔΔΔ
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ΔH f Represents the enthalpy change that occurs when a compound is formed from its constituent elements.
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ΔH° f References to one mole of a compound formed from its constituent elements in their standard state.
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Relationships of Energies of Reactants, Products and Reactions Chapter 16
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Occurs without outside intervention Can occur fast or slow Ex. carbon to diamond
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= disorder The driving force for a spontaneous process is an increase in entropy Has to do with the probability everything is in order
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Higher the positional probability the larger the entropy, +S Increases going from a solid to a liquid, to a gas Increases the larger the volume you have
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In any spontaneous process there is always an increase in the entropy of the universe It occurs in one direction. ∆S univ = ∆S sys + ∆S Surr +∆S univ = process is spontaneous in direction written -∆S univ = spontaneous reverse direction
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1) The sign ∆S surr depends on the direction of the heat flow - ∆S surr = endothermic + ∆S surr = exothermic
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2) The magnitude of ∆S depends on temperature. -The impact of the transfer of energy as heat to and from the surroundings has greater impact at lower temperatures.
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∆H = heat flow = change in enthalpy -∆H sys = endothermic +∆H sys = exothermic
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∆S surr = - ∆H / T *the minus sign changes the point of view from the system to the surroundings - For constant pressure and temperature
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∆G = ∆H -T∆S H = enthalpy T = temperature in Kelvin (constant) S = entropy
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A reaction is spontaneous if ∆G is negative and carried out under constant pressure and temperature.
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The change in positional entropy is dominated by the relative #’s of molecules of gaseous products and reactants
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1) N 2 + 3H 2 2NH 3 2) H 2 2H 3) 4NH 3 + 5O 2 4NO + 6H 2 O
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The entropy of a perfect solids at 0K is zero. An increase in motion is associated with higher entropy value.
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When a solid melts When a solid dissolves When a solid or liquid becomes a gas When a gaseous chemical reaction produces more molecules When the temperature increases
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Given in appendix 4 ∆S o reaction = Σnp S o – Σnr S o
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We cannot measure ∆G directly we must use other measured quantities. The more negative the value of ∆G the further a reaction will go to the right to reach equilibrium
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1) Using the formula ∆G o = ∆H o -T∆S 2) By taking advantage of the fact that ∆G is a state function and solving like Hess’s law
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3) By using ∆G o f, standard free energy of formation ∆G o = Σnp G f o (products)– Σnr G f o (reactants)
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Enthalpy is not affected by pressure Entropy is dependent on pressure because entropy is dependent on volume. S large volume > S small volume so S low pressure > S high pressure
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∆G = ∆G o + RT lnQ ∆G = free energy change for rxn for specified pressure ∆G o = free energy change at standard pressure R = 8.31 J/K * mol T = temp in Kelvin Q = reaction quotient
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The equilibrium point occurs at the lowest value of free energy available to the reaction system
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∆G O = 0 the system is at equilibrium, K = 1, pressure = 1 atm ∆G o 1, pressures of products > 1 atm, pressure of reactants < 1 ∆G 0 > 0 not at equilibrium, K <1, shift left because reactants have less energy
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Free energy can tell us how much work can be done with a given process.
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- ∆G means the amount of free energy available \ to do use work + ∆G is the minimium amount of work that must be expended to make the reaction occur.
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