GenChem6 (Thermochemistry) Flashcards by michael perna

Aspect of chemistry that helps determine whether a reaction is spontaneous

Thermodynamics/thermochemistry

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A reaction that can occur under a given set of conditions without outside assistance is said to be

Spontaneous

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A system that cannot exchange energy or matter with the surroundings, like an insulated bomb reactor

Isolated system

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A system that can exchange energy but not matter with the surroundings, like a steam radiator

Closed System

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A system that can exchange both matter and energy with the surroundings, like boiling water

Open System

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a process that occurs when the temperature of the system remains constant

Isothermal

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A process that occurs when no heat exchange occurs

Adiabatic

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A process that occurs when the pressure of a system remains constant

Isobaric

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A form of energy that can easily transfer to or from a system; the result of a temperature difference between the system and its surroundings

Heat

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Reactions that absorb heat energy are

Reactions that release heat energy are

Endothermic

Exothermic

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This measures heat changes

Calorimetry

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What is the equation for the heat absorbed or released in a given process

q=mcΔT

m=mass, c=specific heat, ΔT=change in temperature

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Type of calorimetry where the volume remains constant

Type of calorimetry where the pressure remains constant

Constant-volume calorimety

Constant-pressure calorimetry

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What is the equation for measuring the q of a reaction with constant volume-calorimetry?

qrxn=-(qwater+qsteel)

q=mcΔT

Note that q of the entire system =zero (for review, page 352)

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Properties whose magnitude depends only on the initial and final states of the system, and not on the path of the change, are known as

State Function

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What are the state functions? (7)

Pressure, temperature, volume, enthalpy (H) entropy (S), free energy (G) and internal energy (E or U)

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What are standard conditions for measuring the enthalpy, entropy, and free energy of a reaction?

25 degrees C and 1 atm

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A substance in its most stable form under standard conditions is said to be in its

Standard State

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The term to express heat changes at constant pressure (typically 1 atm)

Enthalpy

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What is the equation for the enthalpy change of a reaction using standard heat of formation?

ΔH(rxn)=H(prod) - H(react)

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A positive ΔH corresponds to anexothermic/endothermic process

A negative ΔH corresponds to an endothermic/exothermic process

endothermic

exothermic

Defined as the enthalpy change that would occur if one mole of a compound were formed directly from its elements in their standard states

ΔH(f), enthalpy of formation

What is the ΔH(f) of an element in its standard state

Defined as the hypothetical enthalpy change that would occur if the reaction were carried out under standard conditions

ΔH°(rxn)

What is the formula for ΔH°(rxn) using standard heat of formation?

ΔH°(rxn)=sum of ΔH°f(prod) - sum of ΔH°f(react)

What value is used for Hess's law

heat of vaporization, ΔH°(vap)

an average of the energy required to break a particular type of bond in one mole of gaseous molecules Bond breakage is always exothermic/endothermic

Bond Dissociation energy endothermic

There is one more ΔH° value, what is it.

Heat of combustion

Defined as a measure of the disorder, or randomness, of a system. What are the units of it?

Entropy J/K or cal/K (energy/temperature)

A system reaches its maximum entropy at ______, a state in which no observable change takes place as time goes on. What is the equation for ΔS(universe) ΔS(universe) is _______ for a reversible process

ΔS(universe) = ΔS(system) + ΔS(surroundings) = 0 ΔS(universe)=0

The thermodynamic state function that combines the two factors that affect to spontaneity of a reaction (ΔH and ΔS), it represents the maximum amount of energy released by a process, occurring at constant temperature and pressure, that is available to perform useful work.

G (Gibbs free energy)

What is the equation for ΔG

ΔG=ΔH-TΔS Get Higher Test Scores

What does TΔS represent?

The total amount of heat absorbed by a system when its entropy increases reversibly

Is free energy at a minimum or maximum at equilibrium? What range of G can a reaction occur spontaneously?

Free energy is at a minimum in the equilibrium state ΔG<0 (negative values)

If ΔG is zero, the system is in a state of What equation can be used in the circumstance If ΔG is positive, the reaction is

equilibrium ΔH=TΔS non-spontaneous, but spontaneous in the reverse direction

If ΔH is negative and ΔS is positive, what can be said about the spontaneity of the reaction?

Spontaneous at all temperatures

If ΔH is positive and ΔS is negative, what can be said about the spontaneity of the reaction?

Non-spontaneous at all temperature

If ΔH is positive and ΔS is positive, what can be said about the spontaneity of the reaction?

Spontaneous at high temperatures

If ΔH is negative and ΔS is negative, what can be said about the spontaneity of the reaction?

Spontaneous at low temperatures

What does the rate of a reaction depend upon?

Activation energy, not ΔG

What are the parameters of standard free energy, or ΔG°

25°C, 1atm, all concentrations at 1M

The free energy change that occurs when 1 mol of a compound in its standard state is formed from its elements in their standard states under standard conditions is

ΔG°(f), standard free energy

The standard free energy of formation of any element in its most stable state/form is

The free energy change that occurs when a reaction is carried out under standard state conditions, ie when th ereactants in their standard states are converted to produts in their standard states at standard conditions of T and P

ΔG°(rxn) or the standard energy of a reaction ex: conversion of C(diamond) to C(graphite) is spontaneous, but very slow.

What is the equation for ΔG°(rxn)?

ΔG°(rxn) = sum of ΔG°(f) of products- sum of ΔG°(f) of reactants

The equation for ΔG°(rxn) derived from the equilibrium constant is

ΔG°(rxn) = -RT(lnKeq)

Once a reaction commences, the standard state conditions no longer hold. Keq must be replaced by another parameter... the

reaction quotient

What is the equation for the reaction quotient

Q= ([C]^c[D]^d)/([A]^a[B]^b) for equation aA + bB ---> cC + dD

What is the equation for ΔG when standard state conditions no longer hold?

ΔG= ΔG° +RT in Q

For the equation 2C6H6 (l) + 15O2 (g)---> 12CO2(g) + 6H2O(g) + heat is the reaction spontaneous? Which side has greater entropy?

The reaction is spontaneous because heat is released, and there are more moles of gas on the right side of the equation.