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Flashcards in General Chemistry-Thermochemistry Deck (190)
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151

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

152

What is the standard heat of combustion?

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

153

What are oxidents?

Oxygen
Diatomic fluorine
Hydrogen gas will combust chlorine gas

154

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.

155

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.

156

What is the equationn for calculating entropy?

/\S= (Q rev)/ T

157

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

158

What are the units of entropy?

J/mol K

159

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.

160

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

No, Work usually must be done to concentrate energy

161

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.

162

Entropy only is dependent on what?

The difference in entropies of the final and initial states

163

How can the standard entropy change be calculated?

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

164

Gibbs free energy is a combination of what?

Temperature, enthalpy, and entropy

165

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.

166

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

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

167

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

168

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

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

169

A decrease in Gibbs free energy indicates what?

A reaction is spontaneous

170

Movement towards the equilibrium position is associated with what?

A decrease in Gibbs free energy and is spontaneous

171

What is the name for a system that releases energy?

Exergonic

172

What is the name of a system that abosorbs energy?

Endergonic

173

What is another name for energy minimum state?

Equilibrium

174

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

The system will resist any changes to its state

175

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

176

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.

177

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

178

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.

179

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

180

How can you calculate free energies of the reaction?

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