ch 7 - Thermochemistry Flashcards Preview

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Flashcards in ch 7 - Thermochemistry Deck (63)
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1

system

the matter that is being observed - the total amount of reactants and products in a chemical reaction

2

surroundings or environment

everything outside of the system

3

characterizations of systems

isolated: system cannot exchange energy (heat and work) or matter with the surroundings; closed: system can exchange energy (heat and work) but not matter with the surroundings, ex is a steam radiator; open: system can exchange both energy (heat and work) and matter with the surroundings (pot of boiling water)

4

process

when a system experiences a change in one or more of its properties (such as concentrations of reactants or products, temperature, or pressure

5

first law of thermodynamics

delta U = Q - W; delta U = change in internal energy of the system; Q = heat added to the system; W = work done by the system

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isothermal processes

system's temp is constant which implies internal energy of the system (U) is also constant; in this case delta U = 0 and Q = W; P-V graph shows as hyperbolic and work is the area under the graph

7

Adiabatic processes

occur when no heat is exchanged between the system and the environment; thermal energy of the system is constant throughout process. When Q = 0, delta U = -W (change in internal energy of the system is equal to work done on the system); appears hyperbolic on P-V (pressure-volume) graph

8

isobaric processes

occur when the pressure of the system is constant; do not alter the first law; appears as a flat, horizontal line on the P-V (pressure-volume) graph

9

isovolumetric (isochoric) processes

experience no change in volume; no work is performed. W = 0, delta U = Q (change in internal energy is equal to the heat added to the system); vertical line on P-V graph

10

spontaneous process

one that can occur by itself without having to be driven by energy from an outside source

11

state functions

certain macroscopic properties that describe a system in equilibrium state; pressure (P), density, temp (T), volume (V), enthalpy (H), internal energy (U), Gibbs free energy (G), entropy (S)

12

process functions

pathway taken from one equilibrium state to another, quantitatively. The most important of these are work and heat

13

standard conditions

used for measuring the enthalpy, entropy, and Gibbs free energy changes of a reaction: 25 degrees C (298 K), 1 atm pressure, and 1 M concentrations; used for kinetics, equilibrium and thermodynamics problems

14

standard temp and pressure (STP)

used for ideal gas calculations: temp is 0 degrees C (273 K) and pressure is 1 atm.

15

standard state

most stable state of a substance under standard conditions

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standard enthalpy (delta H degree sign), standard entropy (delta S degree sign), standard free energy changes (delta G degree sign)

change in enthalpy, entropy, and free energy that occur when a reaction takes place under standard conditions; degree sign represents zero, as the standard state is used as the "zero point" for all thermodynamic calculations

17

Phase diagrams

graphs that show the standard and nonstandard states of matter for a given substance in an isolated system, as determined by temps and pressures

18

evaporation

also vaporization: liquid to gas; every time liquid loses a high energy particle, temp of remaining liquid decreases; endothermic process for which the heat source is the liquid water

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condensation

gas to liquid; facilitated by lower temp or higher pressure

20

melting or fusion

transition from solid to liquid

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solidification, crystallization, freezing

liquid to solid

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sublimation

solid directly to gas phase

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deposition

from gas to solid

24

temperature

T - related to average kinetic energy of particles of a substance; way we scale how hot or cold something is; average kinetic energy is related to thermal energy (enthalpy); what is hot does not necessarily have a greater thermal energy but when thermal energy increases in a substance so does temp

25

Heat (Q)

the transfer of energy from one substance to another as a result of their differences in temperature; process function; processes that absorb heat are endothermic (delta Q>0) those that release heat are exothermic (delta Q<0); unit of heat is joule (J) or calorie (cal) - one cal = 4.184 J

26

zeroth law of thermodynamics

implies that objects are in thermal equilibrium only when their temps are equal

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calorimetry

process of measuring transferred heat; two basic types are constant-pressure calorimetry and constant-volume calorimetry

28

equation for heat absorbed or released in a given process

q = mc deltaT (q = mcAt); m = mass; c = specific heat of the substance; delta T = change in temp (C or K)

29

specific heat (c)

the amount of energy required to raise the temp of one gram of a substance by one degree Celsius (or one Kelvin)

30

specific heat of H2O

c sub H2O = 1 cal/g x K