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Flashcards in General Chemistry-Thermochemistry Deck (190)
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How is the enthalpy change associated with a reaction given?

/\H degree rxn= sum /\H bonds broken - sum /\H bonds formed= total energy absorbed - total energy released


What is the standard heat of combustion?

/\H degree comb, is the enthalpy change associated with the combustion of a fuel.


What are oxidents?

Diatomic fluorine
Hydrogen gas will combust chlorine gas


What is the second law of thermodynamics?

That energy spontaneously disperses from being localized to becomibg spread out if it is not hindered from doing so.


What is entropy?

The measure of the spontaneous dispersal of energy at a specific temperature: How much energy is spread out, or how widely spread out energy becomes in a process.


What is the equationn for calculating entropy?

/\S= (Q rev)/ T


What do the letters represent in the equation to calculate entropy?

/\S: change in entropy
Q rev: the heat that is gained or lost in a reversible process
T: temperature in kelvins


What are the units of entropy?

J/mol K


What happens when energy is distributed into a system at a given temperature in regards to the entropy?

Its entropy increase. When energy is distributed out of a system, entropy is decreased.


Does concentration of energy happen spontaneously in a closed system? What must be done?

No, Work usually must be done to concentrate energy


Based on the second law of thermodynamics, what happens to energy and entropy in a closed system?

Energy will spontaneously spread out, and entropy will increase if it is not hindered from doing so.


Entropy only is dependent on what?

The difference in entropies of the final and initial states


How can the standard entropy change be calculated?

/\S degree rxn= sum /\S degree f products - sum /\S degree f reactants


Gibbs free energy is a combination of what?

Temperature, enthalpy, and entropy


What is Gibbs free energy a measure of?

A measure of the change in enthalpy and the change in entropy as a system undergoes a process, and it indicates whether a reaction is spontaneous or nonspontaneous. The change in free energy is the maximum amount of energy released by a process occuring at constant temperature and pressure- that is available to perform useful work.


What is the equation for the change in Gibbs free energy?

/\G= /\H - T /\S


What do the letters represent in the /\G equation?

/\G= /\H - T /\S
T: temperature in Kelvins
T/\S: The total amount of energy that is absorbed by a system when its entropy increased reversibly


What mneumonic can be used to remember /\G equation?

Goldfish are (equal sign) horrible without (minus sign) Tarter Sauce


A decrease in Gibbs free energy indicates what?

A reaction is spontaneous


Movement towards the equilibrium position is associated with what?

A decrease in Gibbs free energy and is spontaneous


What is the name for a system that releases energy?



What is the name of a system that abosorbs energy?



What is another name for energy minimum state?



What happens when a system is at equilibrium, in regards to the free energy?

The system will resist any changes to its state


How can you summarize the results of /\G?

If /\G is negative, the reaction is spontaneous
If /\G is positive, the reaction is nonspontaneous
If /\G is zero, the system is in a state of equilibrium


What are the outcomes for the different signs of /\H and /\S in the Gibbs free energy, if the temperature is always positive when using Kelvins?

/\H: + /\S: + Outcome: Spontaneous at high T.
/\H: + /\S: - OUtcome: Nonspontaneous at all T.
/\H: - /\S: + Outcome: Spontaneous at all T.
/\H: - /\S: - Outcome: Spontaneous at low T.


What is important to remember in regards to the rate of a reaction?

The rate of a reaction depends on the activation energy Ea not /\G


What is the standard free energy of formation?

Is the free energy change that occurs when 1 mole of a compound in its standard state is produced from its respective elements in their standard states under standard state conditions. The standard free energy of formation for any element under standard state conditions is by definition zero.


What is standard free energy of a reaction?

Is the free energy change that occurs when that reaction is carried out under standard state conditions; that is , when the reactants are converted to the products at standard conditions of temperature (298K) and pressure 1 atm


How can you calculate free energies of the reaction?

/\G degree rxn= sum /\G degree f products - /\G degree f reactants