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20 Cards in this Set
- Front
- Back
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Which of the following relationships are true? Select all that apply.
ΔE = q + w (under any conditions) ΔE = ΔH + w (at constant P) ΔH = q (at constant P) ΔH = q+w (at constant P) |
ΔE = q + w (under any conditions) ΔE = ΔH + w (at constant P) ΔH = q (at constant P) |
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The first law of thermodynamics states that the total amount of _____ in the universe remains constant. |
energy |
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Hydrogen reacts with oxygen according to the following balanced thermochemical equation: 2H₂(g) + O₂(g) -> 2H₂O(l); ΔH = -572 kJ |
+286 kJ
The coefficients of the reaction have been divided by 2 and the reaction has been reversed. |
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Describe exothermic and endothermic reactions: |
An exothermic reaction is one that releases heat to its surroundings.
The reactants in an endothermic reaction are lower in energy than the products.
If the container of a reaction becomes colder during the reaction, the reaction is endothermic. |
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A _____ function is path independent, meaning that only the initial and _____ conditions are needed to measure the next change that occurred. |
state
final |
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The change in enthalpy (ΔH) is equal to the change in heat (q) when the system is at constant _____. |
pressure |
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"ΔE" indicates a(n) _____ in the internal energy of a system. |
change |
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Describe an enthalpy diagram... |
- The arrow in the enthalpy diagram points from reactants to products.
- In an endothermic reaction, the reactants will be at the bottom of the enthalpy diagram.
- The direction of the arrow in an enthalpy diagram indicates whether a reaction is exothermic or endothermic. |
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a thermochemical equation links a reaction's stoichiometry to its _____ change or ΔH[rxn] |
enthalpy |
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The symbol _____ always indicates heat (or thermal energy), which is transferred as a result of a difference in temperature between a system and its surroundings. |
q |
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Describe the relationship between the volume of a chemical system and work... |
- The expansion of a gas can provide mechanical work.
- A chemical system may do work by the expansion of one or more gaseous products.
- The work done by an expanding gas is calculated using the equation w = -PΔV. |
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The specific heat capacity, abbreviated with the letter _____, is the quantity of _____ required to change the temperature of _____ gram of an object by 1 _____. |
c
energy
1
K |
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An unknown solid is placed in a freezer until it reaches a constant temperature. It is then placed in a room temperature water bath. Identify the sign (+/-) of the temperature change for the solid and for the water bath. |
ΔT[solid] = positive because the solid will gain heat when it is placed in the water bath.
ΔT[water bath] = negative because the solid gains heat from the water bath, which therefore loses heat. |
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When ΔH for a thermochemical equation is negative, that reaction is _____, while a positive value for ΔH is associated with an _____ reaction. |
exothermic
endothermic |
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The sum of all the potential and kinetic energies for all particles in a system is called the total _____ energy (E) of the system. |
internal |
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ΔH will be equal to ΔE if the total number of moles of _____ does not change during a chemical reaction (discounting any small volume change caused by liquids or solids). |
gas |
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A solid initially at 75°C is placed in an insulated water bath initially at 30°C. The temperature reaches 45°C. The change in temperature of the solid was _____ °C, and the change in temperature of the water bath was _____ °C. |
-30
15 |
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_____ is the study of energy and its transformations. |
Thermodynamics |
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Thermodynamic parameters are usually calculated for compounds under _____ conditions, since values tend to vary somewhat with conditions. To be in this state, a gas must have a pressure of 1 _____, and a solution must have a concentration of 1 _____. |
standard
atm
M |
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By definition, the standard enthalpy of formation of a pure _____ in its standard state is equal to 0 kJ/mol. |
element |
