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60 Cards in this Set
- Front
- Back
What is a system?
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The particular part of the universe being studied
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What is everything outside the system considered?
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It is considered the surroundings or environment
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What three things can a system be?
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It can be isolated, closed, or open
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What is an isolated system?
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It cannot exchange energy or matter with the surroundings
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What is a closed system?
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It can exchange energy but not matter with the surroundings
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What is an open system?
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It can exchange energy and matter with the surroundings
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When does a system undergo a process?
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It undergoes a process when one or more of its properties change
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What is a process associated with?
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It is associated with a change of state
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When does an isothermal process occur?
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It occurs when the temperature of the system remains constant
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When does an adiabatic process occur?
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When no heat exchange occurs
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When does an isobaric process occur?
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It occurs when the pressure of the system remains constant
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What is heat?
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It is a form of energy which can easily transfer to or from a system, the result of a temperature difference between the system and its surroundings
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What is heat absorbed by a system considered?
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It is considered positive
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What is heat lost by a system considered?
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It is considered negative
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What are reactions called that absorb heat energy?
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They are endothermic
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What are those that release heat energy?
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They are exothermic
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What is heat measured in?
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It is measured in calories or Joules and more commonly in kcal or kJ
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What is the conversion for calories to Joules?
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1 calorie is equal to 4.184 Joules
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What is the heat (q) absorbed or released in a given process calculated from?
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It is calculated from the equation q = mct
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What occurs in constant-volume calorimetry?
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The volume of the container holding the reacting mixture does not change during the course of the reaction
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What are state functions?
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They depend only on the initial and final states of the system, and not on the path of the change
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What are the state functions?
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Pressure, temperature, volume, enthalpy (H), entropy (S), free energy (G) and internal energy (E or U)
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What is the set for normal conditions?
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25C and 1atm
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What is it used for?
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It is normally used to measure enthalpy, entropy, and free energy of a reaction
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What is a substance called that is in its most stable form under standard conditions?
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It is in its standard state
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What are the changes in enthalpy, entropy, and free energy called when they occur under standard conditions?
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They are called standard enthalpy, standard entropy, and standard free energy
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What do chemists use the term enthalpy (H) for?
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They use it to express heat changes at constant pressure
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What is the change in enthalpy equal to?
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It is equal to the heat absorbed or evolved by the system at constant pressure
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To find the enthalpy change of a reaction, what do you do?
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You subtract the enthalpy of the reactants from the enthalpy of the products
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What does a positive H correspond to?
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It corresponds to an endothermic process
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What does a negative H correspond to?
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It corresponds to an exothermic process
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What is the enthalpy of formation of a compound?
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It is the enthalpy change that would occur if one mole of a compound were formed directly from its elements in their standard states
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What is the standard heat of reaction?
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It is the hypothetical enthalpy change that would occur if the reaction were carried out under standard conditions, ie when reactants in their standard states are converted to products in their standard states at 298K
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What does Hess’s law state?
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Hess’s law states that enthalpies of reactions are additive
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What are the heats of reaction related to?
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They are related to changes in energy associated with the break-down and formation of chemical bonds
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What is bond energy, or bond dissociation energy?
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It is the average of the energy required to break a particular type of bond in one mole of gaseous molecules
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What is entropy (S)?
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It is the measure of the disorder, or randomness, of a system
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What are the units of entropy?
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They are energy/temperature, commonly J/K or call/K
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How does order relate to entropy?
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The greater the order in a system, the lower the entropy
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Do solids have a higher or lower entropy than a gas?
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They have a lower entropy than a gas because individual molecules in the gaseous state are moving randomly, while individual molecules in a solid are constrained in place
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What does the second law of thermodynamics state?
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It states that all spontaneous processes proceed such that the entropy of the system plus its surroundings increases:
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When does a system reach its maximum entropy?
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It reaches it at equilibrium
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What does Gibbs Free Energy do?
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It combines the two factors which affect the spontaneity of a reaction
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What are the two?
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Changes in enthalpy, and changes in entropy
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What does the change in free energy of a system represent?
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It represents the maximum amount of energy released by a process, occurring at constant temperature and pressure
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What is the equation?
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G = H – TS
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What does it mean if G is negative?
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The reaction is spontaneous
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What does it mean if G is positive?
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The reaction is nonspontaneous
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What does it mean if G is zero?
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The system is at equilibrium
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If enthalpy is negative and entropy is positive, is the reaction spontaneous, when?
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It is spontaneous at all temperatures
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If the enthalpy is positive and the entropy is negative, is the reaction spontaneous, when?
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It is nonspontaneous at all temperatures
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If the enthalpy and entropy are both positive, is the reaction spontaneous, when?
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It is spontaneous only at high temperatures
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If the enthalpy and entropy are both negative, is the reaction spontaneous, when?
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It is spontaneous only at low temperatures
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What does the rate of a reaction depend upon?
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It depends upon the activation energy
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Does it depend on G?
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It does not depend on G
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What is the standard free energy
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It is defined as the G of a process occurring at 25C and 1atm pressure, and for which the concentrations of any solutions involved are 1 M
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What is the standard free energy of formation?
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It is 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
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What is the standard free energy of formation of any element in its most stable form?
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Zero
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What is the standard free energy of reaction?
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It is the free energy change that occurs when that reaction is carried out under standard state conditions, i.e., when the reactants in their standard states are converted to the products in their standard states, at standard conditions of T and P
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What is the reaction quotient (Q)?
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It is the products raised to their amounts divided by the reactants raised to their amounts
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