Chapter 5: energy, heat, and work Flashcards Preview

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Flashcards in Chapter 5: energy, heat, and work Deck (93):
1

a complete chemical equation includes a quantitative measure of the

energy produced or consumed

2

thermochemistry is the study of the

relationship between heat and chemical reactions

3

all forms of energy fall into two categories:

kinetic energy and potential energy

4

kinetic energy is energy possessed by matter because it is

in motion

5

the kinetich energy of an object depends on both its

mass (m) and its velocity (v)

6

kinetic energy =

1/2m * v^2

7

The SI unit for energy is the

joule (J)

8

joule=

[(kilogram)(meter)^2] / (second)^2

9

thermal energy is kinetic energy in the form of

random motion of the particles in a sample of matter

10

the greater the temperature of the matter, the ... its particles move and the ...

faster; higher its thermal energy

11

heat is the flow of energy from ... that causes a change in the ...

one object to the other; temperature of the object

12

when heat is added to or removed from a sample, it causes a change in the

temperature of that sample

13

work is the application of a

force across some distance

14

it takes energy to perform .., so like heat, quantities of .. are expressed in units of ...

work; work; joules

15

work can take many forms: ... work, ... work, ... work, ... work, and ... work

mechanical; chemical; gravitational; pressure-volume; electrical

16

potential energy is energy possessed by matter because of its

position or condition

17

.... energy: compounds also possess ... as a result of the ...

chemical; potential energy; forces that hold the atoms together

18

in a chemical reaction, because the chemical energy of the reactants is not the same as that of the products, enrgy is either ... or ... during the reaction, usually in the form of ...

absorbed; released; heat

19

system:

sample of matter

20

the system is the matter of

interest

21

the surroundings are

all other matter

22

surroundings include the

reaction container

23

law of conservation of energy states that the total energy of the ... is ... during a ...

universe; constant; chemical/physical change

24

universe:

system + surroundings

25

energy is often ... the system and the surrooundings

transferred between

26

law of conservation of energy is also referred to as the

first law of thermodynamics

27

if energy transfers between the system and the surroundings, then the total amount of energy contained in the system has

changed

28

energy change =

work + heat

29

exothermic: ... to the surroundings

releases heat

30

endothermic: a reaction that

absorbs heat

31

energy can be considered a

reactant/product

32

SI unit of heat energy is

joule

33

a calorie was originally defined as the amount of heat needed to increase the .... by ..., from .. to ...

temperature of 1 g water; 1 degree celsius; 14.5 degrees C to 15.5 degrees C

34

1 cal =

4.184 J

35

thus, it takes ... J to increase the temperature of 1 g water from 14.5 degrees celsius to 15.5 degrees celsius

4.184 J

36

enthalpy, H, of a system is the measure of the

total energy of the system at a given pressure and temperature

37

enthalpy cannot be measured, but the ... that accompanies a change in the system can be measured

change in enthalpy

38

under conditions of constant pressure and temperature, the quanitity of heat ... at constant temperature and pressure is called the

absorbed/given off by the system; change in enthalpy

39

delta H means

Hfinal - Hinitial

40

if the chemical reaction is exothermic, the system has ..., which means that its enthalpy ... and delta H is ..

lost energy; decreases; negative

41

if the chemical reaction is endothermic, the enrgy of the system ... and the sign of delta H is ...

increases; positive

42

a thermochemical equation is a chemical equation for which

the value of delta H is given

43

the chemical reaction is assumed to occur at .., because delta H is used in the thermochemical equation

constant pressure and temperature

44

the enthalpy is determined by

experiment

45

in a thermochemical equation, delta H assumes that the coefficients refer to

molar quantities

46

it is important to include the ... of every substance in any ...

physical state; thermochemical equation

47

enthalpy changes are part of the ... of a thermochemical equation

Stoichiometry

48

the thermochemical equation expresses the stoichiometric relationship between the ... of any substance in the equation and the ...

number of moles; quantity of heat produced or absorbed in the reaction

49

calorimetry: measurement of the heat ... when the ... occurs

released or absorbed; chemical change

50

calorimeter: the device in which the ... and the ...

reaction takes place; heat is meausred

51

the quantity of heat released or absorbed by the reaction causes a change in the .... which is measured with a ...

temperature of the solution; thermometer

52

for the heat to correspond to the enthalpy change of the system, the calorimeter must be operated at

constant pressure

53

the reaction in the calorimeter proceeds at constant pressure because .. changes little during the course of the experiment

atmospheric pressure

54

the insulation provided by the calorimeter prevents any

transfer of heat into or out of the calorimeter

55

in a calorimetry experiment, the amount of solution must be known because the observed temperature change depends on the

amount of solution present

56

the heat capacity of a sample is the quantity of heat required to

increase the temperature of that object by 1 K

57

heat capacity has units of ... or ..., and is nearly constant for a given substance over...

J/K; J/ degrees C; small ranges of temperature

58

the specific heat is the heat needed to ...

increase the temperature of a 1-g sample of the material by 1 K

59

1 =

m*Cs*deltaT

60

q is

heat in joules

61

m is

mass in grams

62

Cs is

specific heat of sample

63

(assumptions in calorimetry calculations) the heat required to change the temperature of the vessel, stirrer, and thermometer is

sufficiently small to be ignored

64

(assumptions in calorimetry calculations) the specific heat of the solution, as long as it is dilute, is the

same as that of water, 4.184 J/gK

65

a state function is any ... that is determeined by the ..

property of a system; present conditions of the system

66

the state function is independent of how the

system got to that set of conditions

67

the enthalpy, and the change in enthalpy, of a chemical system is a

state function

68

the value of delta H for a process does not depend on how the

process occurred

69

the delta H is only dependent of the ... of the system and the ... of the system

initial state; final state

70

in thermochemical equations, the coefficients refer to molar amounts, so

fractional coefficents can be used

71

energy-level diagrams are ... graphs

one-dimensional

72

an energy-level diagram is a representation of the relative ... of the ...

enthalpies; reactnats and products of a reaction

73

reversing the direction of a chemical reaction ... on the reaction's deltaH

changes the sign

74

Hess's law: calculating the enthalpy change in an overall chemical reaction by

summing the enthalpy changes of each step

75

the properties that govern the combination of thermochemical equations are natural consequences of ... and the fact that ...

the law of conservation of energy; enthalpy is a state function

76

the change in enthalpy for an equation obtained by adding two or more thermochemical equations is the sum of the

enthalpy changes of the added equations

77

the enthalpy change is an ... that depends on the amounts of the substances that react

extensive

78

hess's law lets us calculate the enthalpy change for one reaction from

thermochemical equations for others

79

enthalpy change for any reaction is influenced by the

pressure and the temperature

80

standard state of a substance is the ... at ... and the ...

pure form; one atmosphere pressure; designated temperature (usually 298.15 K or 25.0 degrees C)

81

standard enthalpy change is an enthalpy change in which all

reactants and products are in their standard states

82

the symbol for standard enthalpy change is

ΔH°

83

° means that all reactants and products are in the standard state of

1 atm pressure and 298.15 K

84

a formation reaction is a chemical reaction that makes

one mole of a substane from its constituent elements in their standard states

85

the enthalpy change for a formation reaction is symbolized by

ΔHf°

86

the subscript f stands for

formation

87

ΔHf° is called

standard enthalpy of formation

88

the ΔHf° of all elements in their standard states is

zero

89

ΔH°rxn =

∑mΔHf° [products] - ΣnΔHf° [reactants]

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m is the number of moles of each

product

91

n is the number of moles of each

reactant

92

the reactants contribute the ... of their enthalpies of formation, whears products contribute the ... of their enthalpies of formation

negative; positive

93

enthalpy of combustion: the energy change for a ...

combustion reaction