Flashcards in General Chemistry-Thermochemistry Deck (190)
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91
What is the definition of temperature?
(T) Related to the average kinetic energy of the particles of a substance. Temperature is the way that we scale how hot or cold something is.
92
What are the different scaes used to measure temperature?
Fahrenheit, Celsius, Kelvin
93
What is thermal energy?
Or Enthalpy is the average kinetic energy of the particle in a substance
94
How do you calculate total thermal energy content?
Must know how much substance is present
95
When a substance's thermal energy increases, what happens?
It's temperature also increases
96
Does something that is hot always have greater thermal energy? Why?
No, it depends on the amount of substance
97
How was the Kelvin scale determined?
Via the third law of thermodynamics, which elucidated that there is a finite limit to temperature below which nothing exist. There can be no temperature below 0 K because, by definition the system is said to be unable to lose any more heat energy.
98
What is the definition of heat?
(Q) is the transfer of energy from one substance to another as a result of their differences in temperature.
99
What does the zeroth law of thermodynamics imply?
Objects are in thermal equilibirum only when their temperatures are equal.
100
Heat is a process function or a state function?
Process function
101
What does the 1st law of thermodynamics state?
The change in the total internal energy (/\U) of a system is equal to the amount of heat (Q) transfered to the system minus the amount of work (W) done by the system: /\U= Q-W
102
Why can you assess the transfer of heat through any process regardless of work done?
Because the heat and work are measured independently
103
What units are used to measure heat?
The unit of energy: Joule (J) or calorie (cal)
104
What is the conversion of 1 cal to joules?
1 cal= 4.184 joules
105
What is equivalent to heat that is what the MCAT assumes on most thermodynamic problems?
Enthalpy (/\H) is equivalent to heat under constant pressure
106
When a substance goes through a endo or exothermic reaction, what also happns?
Heat energy will be exchanged between the system and the environment
107
What is calorimetry?
The process of measuring transferred heat
108
What are the two basic types of calorimetry?
Constant-pressure calorimetry
Constant-volume calorimetry
109
What equation is used to calculate the heat absorbed or released in a given process?
q = mc(/\T)
110
What do the letters represent in the heat absorption equation?
m: mass
c: the specific heat of the substance
/\T: Change in temperature (in celsius or kelvins)
111
What is specific heat?
The amount of energy required to raise the temperature of one gram of a substance by one degree celsius (or one Kelvin)
112
What is the specific heat of H2o (l)?
1 cal/gK
113
What is heat capacities?
The product mc (mass times specific heat)
114
What is an example of a constant pressure calorimeter?
An insulated container covered with a lid and filled with a solution in which a reaction or physical process, such as dissolution, is occurring. The incident pressure, which is atmospheric pressure, remains constant throughout the process, and the temperature can be measured as the reaction progresses. There should be sufficient thermal insulation (such as styrofoam) to ensure that the heat being measured is an accurate representation of the reaction, without gain or loss of heat to the environment.
115
What is another term for bomb calorimeter?
Decomposition vessel
116
Bomb calorimeter is used in what type of calorimetry?
Constant-volume calorimetry
117
How are constant-volume calorimetry reactions done?
A sample of matter is placed in the steel decomposition vessel, which is then filled with almost pure oxygen gas. The decomposition vessel is then placed in an insulated container holding a known mass of water. the contents of the decomposition vessel are ignited by an electric ignition mechanism, the materal combusts in the presence of the oxygen, and the heat that evolves is the heat of the combustion reaction.
118
Why is no work done in constant-volume calorimetry?
Because W=P(/\V), no work is done in an isovolumetric process.
119
Why can constant-volume be considered isolated from the rest of the world?
Because of the insulation.
120
