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Chemistry > Chapter 5 - Thermochemistry > Flashcards

Chapter 5 - Thermochemistry Flashcards

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1
Q

define thermochemistry

A

the study of the energy changes that accompany physical or chemical changes in matter

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2
Q

define energy

A

the ability to do work

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3
Q

SI units for energy

A

Joules (J)

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4
Q

define work

A

the amount of energy transferred by a force over a distance

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5
Q

SI units for work

A

Joules (J)

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6
Q

how can energy be classified?

A

as potential energy or kinetic energy

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7
Q

define potential energy

A

the energy of a body of system due to its position or composition

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8
Q

define kinetic energy

A

the energy of an object due to its motion

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9
Q

what is the energy associated with chemical bonds?

A

potential energy

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10
Q

what are chemical bonds?

A

attractive forces between the nucleus of one atom or ion and the negative charges of the electrons in the other atom or ion

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11
Q

what is the amount of energy released/absorbed in a chemical reaction equal to?

A

the difference between the potential energy of the bonds in the reactants and the potential energy of the bonds in the products

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12
Q

define thermal energy

A

the total quantity of kinetic and potential energy in a substance

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13
Q

what does the quantity of thermal energy in a substance depend on?

A

how fast its entities are moving

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14
Q

what are entities?

A

atoms, molecules, ions, polyatomic ions

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15
Q

when a substance absorbs thermal energy, what happens?

A

its entities move at a greater speed, and the substance warms up

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16
Q

what happens when a substance releases thermal energy to its surroundings?

A

its entities move more slowly, and the substance cools

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17
Q

define heat

A

a verb that refers to the transfer of thermal energy from a warm object to a cooler object

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18
Q

define temperature

A

a measure of the average kinetic energy of entities in a substance

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19
Q

which has a higher temperature and why: iceberg vs hot cup of water

A

the hot cup of water has a higher temperature because the average water molecule in a cup of hot water has a higher temperature than the average water molecule in an iceberg

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20
Q

which has more thermal energy and why: iceberg vs hot cup of water

A

the iceberg has more thermal energy because the iceberg contains more water molecules

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21
Q

define law of conservation of energy

A

energy cannot be created or destroyed

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22
Q

what can energy only do?

A

be converted from one form to another

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23
Q

how do chemists divide the universe?

A

chemical system, its surroundings

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24
Q

define chemical system

A

a group of reactants and products being studied

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25
Q

define surroundings

A

all the matter that is not part of the system

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26
Q

what two ways can chemical systems be classified?

A

open, closed

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27
Q

define open system

A

a system in which both matter and energy are free to enter and leave the system

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28
Q

define closed system

A

a system in which energy can enter and leave the system, but matter cannot

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29
Q

what happens with the chemical bonds in a chemical reaction?

A

chemical bonds in the reactants are broken, new bonds are formed to produce the products

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30
Q

potential energy of entities in a stable structure vs potential energy of individual isolated atoms

A

potential energy of entities in a stable structure is lower

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31
Q

what does bond breaking and formation require from energy

A

bond breaking requires energy while bond formation releases energy

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32
Q

what do entities in a stable structure include?

A

atoms, ions, or molecules in an ionic compound

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33
Q

define exothermic

A

releasing energy to the surroundings

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34
Q

when is more energy released in an exothermic reaction?

A

more energy is released from the formation of new bonds of products than is required to break the bonds in the reactants

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35
Q

potential energy and bonds of products vs reactants in exothermic reaction?

A

products have lower potential energy and stronger bonds than reactants

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36
Q

what happens when an exothermic reaction releases energy?

A

the temperature of the surroundings increase

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37
Q

define endothermic

A

absorbing energy from the surroundings

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38
Q

what occurs in an endothermic reaction with the chemical system?

A

absorbs energy from its surroundings and increases its potential energy

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39
Q

potential energy and bonds of products vs reactants in endothermic reaction

A

products have higher potential energy and weaker bonds than the reactants

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40
Q

what type of reaction can a chemical reaction take?

A

endothermic or exothermic

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41
Q

what type of reaction can a nuclear reaction take?

A

exothermic

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42
Q

name two nuclear reactions involving large quantities of energy

A

fusion and fission

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43
Q

define fusion

A

the process of combining two or more nuclei of low atomic mass to form a heavier, more stable nucleus

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44
Q

define fission

A

the process of using a neutron to split a nucleus of high atomic mass into two nuclei with smaller masses

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45
Q

what types of changes can a potential energy change result from?

A

any physical, chemical, or nuclear change

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46
Q

magnitudes of potential energy changes from lowest to highest

A

phase change, chemical change, nuclear change

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47
Q

what is the symbol for specific heat capacity?

A

c

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48
Q

define specific heat capacity

A

the quantity of thermal energy required to raise the temperature of 1 g of a substance by 1 ℃

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49
Q

SI units for specific heat capacity

A

J/(g・℃)

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50
Q

what is the specific heat capacity of liquid water?

A

4.18 J/(g・℃)

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51
Q

specific heat capacity of water vs sand and what this causes

A

specific heat capacity of water is higher than sand so it takes less to raise the temperature of sand and it will become hotter than the water

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52
Q

define calorimetry

A

the experimental process of measuring the thermal energy change in a chemical or physical change

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53
Q

define calorimeter

A

a device that is used to measure thermal energy changes in a chemical or physical change

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54
Q

what does a calorimeter consist of?

A

a well insulated reaction chamber, a tight fitting cover with insulated holes for a thermometer, and some mechanism to stir the contents of the calorimeter

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55
Q

what does using an insulated chamber minimize?

A

energy loss to the surroundings

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56
Q

what is a coffee cup calorimeter composed of?

A

polystyrene cover and two cups, inner cup holds chemical system and a liquid, usually water, outer cup provides additional insulation

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57
Q

how are changes in the thermal energy of the chemical system detected in a coffee cup calorimeter?

A

through temperature changes in the water

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58
Q

2 assumptions of insignificance made when using a coffee cup calorimeter

A

any thermal energy transferred from the calorimeter to the outside environment is negligible, any thermal energy absorbed by the calorimeter itself is negligible

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59
Q

assumption of calculations made when using a coffee cup calorimeter

A

all dilute, aqueous solutions have the same density and specific heat capacity as water

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60
Q

density of water

A

1.00 g/mL

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61
Q

when are these assumptions valid?

A

for chemical or physical changes that take place in water or a dilute, aqueous solution

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62
Q

what is q

A

the total amount of thermal energy released or absorbed by a chemical system

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63
Q

what does the magnitude of q depend on?

A

the mass of the substance, the specific heat capacity of the substance, the temperature change experienced by the substance as it warms or cools

64
Q

formula to calculate q

A

q = mcΔT

65
Q

what does the symbol m stand for

A

mass of the substance

66
Q

formula to calculate ΔT

A

ΔT = Tfinal - Tinitial

67
Q

what happens when q has a negative value to thermal energy, reaction change, and water

A

system transfers thermal energy to the surroundings, reaction change is exothermic, temperature of water increases

68
Q

what happens when q has a positive value to thermal energy, reaction change, and water

A

system absorbs thermal energy from its surroundings, reaction change is endothermic, temperature of the water decreases

69
Q

in a coffee cup calorimeter, what is the surroundings?

A

the water

70
Q

what substances contain a certain amount of thermal energy?

A

any substance undergoing a physical or chemical change

71
Q

what is the symbol for enthalpy?

A

H

72
Q

define enthalpy

A

the total amount of thermal energy in a substance

73
Q

how is enthalpy measured?

A

cannot be measured

74
Q

what is the symbol for enthalpy change?

A

ΔH

75
Q

define enthalpy change

A

energy released to or absorbed from the surroundings during a chemical or physical change

76
Q

how is enthalpy change measured?

A

using calorimetry data

77
Q

formula for enthalpy change equal to thermal energy in and out of the system

A

ΔHsystem = |qsystem|

78
Q

what condition needs to be in place to use the formula ΔHsystem = |qsystem|

A

pressure remains constant

79
Q

for a chemical reaction, what is the formula for enthalpy change?

A

ΔH = Hproducts - Hreactants

80
Q

when is the enthalpy change positive, and what kind of reaction is this?

A

products have a greater enthalpy than reactants, endothermic reaction

81
Q

when is the enthalpy change negative and what kind of reaction is this

A

products have a lower enthalpy than reactants, exothermic reaction

82
Q

in an exothermic reaction, explain what happens with the kinetic and potential energy of the chemical system and the surroundings

A

chemical system goes from high potential energy to low potential energy, surroundings goes from low kinetic energy to high kinetic energy

83
Q

what is the symbol for molar enthalpy change?

A

ΔHr

84
Q

define molar enthalpy change

A

the enthalpy change associated with a physical, chemical, or nuclear change involving 1 mol of a substance

85
Q

SI units for molar enthalpy change

A

J/mol

86
Q

what does the subscript r represent in the molar enthalpy change

A

reaction type

87
Q

how to balance equations for thermochemical reaction

A

relevant substance has coefficient of 1, other substances may have fractional coefficients

88
Q

4 types of thermochemical reaction

A

solution, combustion, vaporization, formation, neutralization

89
Q

subscript symbol for solution thermochemical reaction

A

sol

90
Q

subscript symbol for combustion thermochemical reaction

A

c

91
Q

subscript symbol for vaporization thermochemical reaction

A

vap

92
Q

subscript symbol for neutralization thermochemical reaction

A

neut

93
Q

explain solution reaction

A

solid reactant to aqueous products with appropriate charge on products

94
Q

explain combustion reaction

A

gas and oxygen gas forms carbon dioxide gas and liquid water

95
Q

explain vaporization reaction

A

liquid turns to gas

96
Q

explain formation reaction

A

solid reactants unless they are gas forms liquid product

97
Q

explain vaporization reaction

A

aqueous base and acid forms aqueous product and liquid water

98
Q

relevant substance of vaporization reaction

A

per mole of acid or base

99
Q

which reactions don’t have relevant substance in reactant

A

formation

100
Q

what does the enthalpy change depend on

A

quantity of matter than undergoes the change

101
Q

how much more energy is needed to convert 1 L of liquid water to water vapour than 500 mL

A

2 times

102
Q

formula to calculate enthalpy change for substances other than 1 mol

A

ΔH=nΔHr

103
Q

which substances undergo a change in enthalpy

A

all those in chemical reactions

104
Q

what is a chemical equation that describes the enthalpy change of a reaction

A

thermochemical reaction

105
Q

what are the two ways to write a thermochemical reaction

A

adding energy term as product/reactant, writing enthalpy change after balanced equation where ΔH = +/- enthalpy change

106
Q

what is indicated by an energy term added as a product and what type of reaction is this

A

indicates energy released by the chemical system, exothermic reaction

107
Q

what is indicated by an energy term added as a reactant and what type of reaction is this

A

indicate energy absorbed by the chemical system, endothermic reaction

108
Q

2 ways to represent thermochemical enthalpy changes

A

energy terms, potential energy diagrams

109
Q

define potential energy diagram

A

a graphical representation of the energy transferred during a physical or chemical reaction

110
Q

in a chemical reaction, what has potential energy?

A

both products and reactants

111
Q

potential energy symbol for potential energy diagram

A

Ep (KJ)

112
Q

x-axis, y-axis and title of potential energy diagram

A

x-axis: reaction progress, y-axis: potential energy, potential energy symbol, title: potential energy diagram during a(n) __ reaction

113
Q

how do you show change from the arrow of potential energy diagrams

A

use molar enthalpy change symbol = +/- change

114
Q

in a potential energy diagram, what reaction is it when arrow goes down?

A

exothermic

115
Q

in a potential energy diagram, what reaction is it when arrow goes up?

A

endothermic

116
Q

what does the bond energy of a single covalent bond breaking mean?

A

the energy required to break one mol of the covalent bond into 1 mol of one atom and 1 mol of another

117
Q

what does the bond energy mean when a covalent bond forms?

A

the amount of energy released

118
Q

how do we use bond energies

A

can calculate enthalpy change of an chemical reaction f we know the bond energies of the chemical bonds of the reactants and products

119
Q

define bond dissociation energy

A

the energy required to break a given chemical bond

120
Q

why are bond dissociation energies given as average bond energies?

A

the energy depends on the types of atoms and bonds in the same molecule

121
Q

which has larger bond energies: multiple bonds or single bonds

A

multiple bonds

122
Q

what is suggested by multiple bonds having larger bond energies?

A

multiple bonds are stronger

123
Q

what is the relationship between number of bonds between atoms and bond length

A

as the number of bonds increase, the bond length shortens

124
Q

what is meant by number of bonds

A

number of electrons shared

125
Q

what is meant by bond length

A

distance between the nuclei

126
Q

what must happen first in a chemical reaction

A

bonds must break

127
Q

what must happen for bonds to break, what is the reaction type, and what is the sign of the energy term

A

energy must be added, an endothermic process, energy terms are positive

128
Q

what must happen for bonds to form, what is the reaction type, and what is the sign of the energy term?

A

energy is released, an exothermic process, energy terms are negative

129
Q

what is the middle step of the enthalpy change of a reaction using bond energies

A

ΔH = sum of energies required to break old bonds (positive) - sum of energies released in the formation of new bonds (negative)

130
Q

what is the equation for enthalpy change using bond energies

A

ΔH = Σn x D (bonds broken) - Σn x D (bonds formed)

131
Q

what does the symbol D mean and what is the sign?

A

bond energy, always positive

132
Q

what are the units of D

A

KJ/mol

133
Q

why can we use bond energies?

A

because bond energies of similar bonds are nearly the same in different molecules and they provide a good approximation of the actual bond energy value

134
Q

what is the change in enthalpy of a chemical process independent of?

A

the path taken

135
Q

what does the change in enthalpy being independent of the path taken mean?

A

going from an initial set of reactants to a final set of products in one step or a series of steps has the same enthalpy change

136
Q

what happens if you add the thermochemical equations used in a series of steps, including the sum of enthalpy changes?

A

you get the overall, net reaction and the enthalpy change for the net reaction

137
Q

define hess’s law

A

the enthalpy change for the conversion of reactants to products is the same whether the conversion occurs in one step or several steps

138
Q

how is hess’s law useful?

A

useful to study energy changes in chemical reactions that cannot be analyzed using calorimetry

139
Q

what 2 rules must you follow when using Hess’s rule to calculate enthalpy change?

A

if you reverse the chemical reaction, you must also reverse the sign of ΔH. if the coefficients in a balanced equation are multiplied by a factor, the value of ΔH is multiplied by the same factor

140
Q

what is proportional to the magnitude of ΔH

A

the number of moles of reactants and products in a reaction

141
Q

define formation equations

A

represent the formation of a compound from its elements

142
Q

define standard enthalpy of formation

A

the change in enthalpy that accompanies the formation of 1 mol of a compound from its elements in the standard state

143
Q

what is the symbol for standard enthalpy of formation

A

ΔHf°

144
Q

define standard state

A

the most stable form of a substance under stable conditions

145
Q

what is the standard ambient temperature and pressure

A

25 degrees celsius and 100 kPa

146
Q

what is the standard state of most elements

A

solid

147
Q

which elements are gases in their standard state?

A

diatomic elements, and noble gases

148
Q

list the diatomic elements

A

hydrogen, oxygen, nitrogen, fluorine, chlorine

149
Q

which elements are liquids in their standard state?

A

mercury, bromine

150
Q

what is the standard state for a substance in a solution?

A

1 mol/L

151
Q

what does the degree sign for standard enthalpy of formation mean?

A

the process takes place under standard conditions

152
Q

what is the standard enthalpy of formation of an element in its standard state?

A

0

153
Q

why is the standard enthalpy of formation of an element in its standard state 0?

A

an element is in its most fundamental form at standard conditions

154
Q

what must you do to balance the standard enthalpy of formation equation?

A

1 mol of the product

155
Q

type of reaction of enthalpies of formation

A

exothermic or endothermic

156
Q

how do we calculate standard enthalpies of reaction from standard enthalpies of formation formula?

A

ΔHr° = ΣnproductsΔH°products - ΣnreactantsΔH°reactants

Chemistry (6 decks)

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