thermochemistry. energy - "the capacity to do work" unlike matter, energy is known and...

Thermochemistry

ENERGY - the capacity to do work

bull Unlike matter energy is known and recognized by its effectsndash it cannot be seen touched smelled or weighed

bull types of energyndash radiant

(solar energy) energy from the sunndash thermal

the energy associated with the random motion of atoms and molecules (measured by temperature)

ndash chemical

energy stored within the structural units of chemical substancesndash potential

energy available by virtue of an objects position

Conservation of Energy

bull the total quantity of energy in the universe is assumed constant

bull Energy cannot be created or destroyed

bull When one form of energy disappears some other form of energy (of equal magnitude) must appear

ndash The above statements are all saying the same thing

All forms of energy can theoretically convert to other forms of energy

bull Chemical reactions are often utilized in our day-to-day lives not for the products that they produce but for the converted energy that results (ie fuels like natural gas - a chemical reaction results in the transfer of Chemical energy to thermal energy)

bull We do not use the products of the reactionndash Carbon Dioxidendash Water

Hence why there is so much pollution

THERMOCHEMISTRY

ndash Thermochemistry - the study of heat change in chemical reactions

ndash Heat - is the transfer of thermal energy between two bodies that are at different temperatures

Systems and Surroundings (parameters)

ndash When looking at chemical reactions we have to define the system

bull

bull 3 types of systems of Thermochemistry

1open system

2closed system

3isolated systemndash the rest of the universe (outside the system is

called the surroundings)

bull open systems can exchange mass and energybull closed systems allow the transfer of energy (he

at) but not massbull isolated systems do not allow transfer of either

mass or energy

HYDROGEN EXPLOSION - combustion

bull Is this reaction taking place in an open closed or isolated system

bull the reacting mixture is the system (hydrogen oxygen and water molecules) everything else is the surroundings

bull This is exothermic because it is a combustion reaction (thermal energy leaves during this and all other exothermic reaction -- a lot of thermal energy is released in this example）

)(2)(2 222 lOHOgH

open system

Liberating Hydrogen from HClbull Is this reaction taking place in an open closed o

r isolated system

22 HZnClHClZn The gas (hydrogen) is collected and therefore never leaves the system All the matter remains in the system

This is a closed system This system is both exothermic and endothermic Heat is released to the surroundings as Zinc and Chlorine bond together but as hydrogen disassociates from the Chlorine energy is taken in

Whats an example of a chemical reaction occurring in a closed system

bull Examples of Closed Systems

Equations

VP-qE

EQUATIONSCOMBINING

out going means -

in going means remember

wqE

WORKand HEAT

J 1013atm L 1 -convert oremember t

system ain n nexpansiocompressio

VPw

PRACTICE QUESTION

The work done to compress a gas is 74 J As a result 26 J of heat is given off to the surroundings Calculate the change in energy of the gas

Which equation should you use to solve

ANSWER 48 J

Enthalpy (H)

H V

constant remains pressure

ssystem theheat when in change

theof value theas of thought becan

H

VPEH

Most reactions are constant-pressure process Therefore so we can equate the heat change to the change in H

CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem

Determine the amount of heat (in kJ) given off when 126 x 10^4 g of NO2 are produced according to the equation

kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ

Practice Problem (for change in Energy)

bull If 20 moles of H2O(g) are converted to H2(g) and O2(g) against a pressure of 10 atm at 125 degrees celsius what is the change in Energy

molkJH

OgHgOH

6483

)(2)(2 222

Calorimetry - the measurement of heat changebull a calorimeter is an insulate

d closed container that creates an ISOLATED SYSTEM

bull a specific quantity of water surrounds a system carrying out a reaction

bull during the reaction heat leaves the system and is absorbed by the surrounding water

bull by recording temperature change the heat generated by a reaction can be recorded

Calorimetrybull Either heat capacity or specific heat must be a

pplied to find a substances change in heatbull Remember

heat capacity specific heat

(C) = m x (s)

tmsqtCq

cc

J

g

J g

bull Heat Capacity ndash heat needed to raise a certain quanity of a su

bstance 1 degree (celsius)

bull Specific Heat ndash the heat needed to raise a 1 gram of a specifi

c substance 1 degree (celsius)

Calorimeter 1 - Constant-Volume Calorimiter (The BOMB Calorimeter)

bull Purpose to collect data on combustible reactions

bull When adding heat to a substance in a Constant-Volume Calorimeters the pressure will increase because the volume has remained the same

bull The substance inside cannot expand


bull Change of heat of a reaction is qrxn

bull Since the a calorimeter is an isolated system the change in heat of the calorimeter plus water is equal but opposite to the change of heat in the reaction

qsystem = qcal + qrxn = 0Meaning

qcal = -qrxn

Practice Questionbull A quantity of 1435 naphthalene (C10H8) is

burned in a calorimeter The water temp rises from 2028 to 2595 degrees celsius If the heat capacity (C) is 1017 kJcelsius calculate the molar heat combustion of C10

H8bull What is being asked herebull How much heat per mole of napthalene is released into t

he calorimeterTo do

bull Need to figure out how much heat is generated by the combustionbull Need to convert this total heat to q per mole (kJmol)

Practice Question

bull 1922g of methanol (CH3OH) was burned in a calorimeter The temp of water rose by 42 degrees celsius The heat capacity of the system (calorimeter plus water) is 104 kJcelsius Calculate the molar heat of the combustion of methanol

Calorimeter 2 - Constant-Pressure Calorimeter

bull Measures heat changes for non-combustible reaction (ie acid-base reactions)

bull Since the pressure remains the same change in enthalpy equals that to the change in heat

bull Also isolated and filled with water

Specific Heat will be used in calculations Waters specific heat is 4184 Jg(celsius)

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ENERGY - the capacity to do work

bull Unlike matter energy is known and recognized by its effectsndash it cannot be seen touched smelled or weighed

bull types of energyndash radiant

(solar energy) energy from the sunndash thermal

the energy associated with the random motion of atoms and molecules (measured by temperature)

ndash chemical

energy stored within the structural units of chemical substancesndash potential

energy available by virtue of an objects position










THERMOCHEMISTRY





bull


1open system

2closed system





mass or energy





)(2)(2 222 lOHOgH

open system


r isolated system





Equations

VP-qE

EQUATIONSCOMBINING

out going means -


wqE

WORKand HEAT



VPw

PRACTICE QUESTION



ANSWER 48 J

Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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THERMOCHEMISTRY





bull


1open system

2closed system





mass or energy





)(2)(2 222 lOHOgH

open system


r isolated system





Equations

VP-qE

EQUATIONSCOMBINING

out going means -


wqE

WORKand HEAT



VPw

PRACTICE QUESTION



ANSWER 48 J

Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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bull


1open system

2closed system





mass or energy





)(2)(2 222 lOHOgH

open system


r isolated system





Equations

VP-qE

EQUATIONSCOMBINING

out going means -


wqE

WORKand HEAT



VPw

PRACTICE QUESTION



ANSWER 48 J

Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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mass or energy





)(2)(2 222 lOHOgH

open system


r isolated system





Equations

VP-qE

EQUATIONSCOMBINING

out going means -


wqE

WORKand HEAT



VPw

PRACTICE QUESTION



ANSWER 48 J

Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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)(2)(2 222 lOHOgH

open system


r isolated system





Equations

VP-qE

EQUATIONSCOMBINING

out going means -


wqE

WORKand HEAT



VPw

PRACTICE QUESTION



ANSWER 48 J

Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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r isolated system





Equations

VP-qE

EQUATIONSCOMBINING

out going means -


wqE

WORKand HEAT



VPw

PRACTICE QUESTION



ANSWER 48 J

Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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Equations

VP-qE

EQUATIONSCOMBINING

out going means -


wqE

WORKand HEAT



VPw

PRACTICE QUESTION



ANSWER 48 J

Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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Enthalpy (H)

H V




H

VPEH


CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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CHANGE IN H

0H EXOTHERMIC

0H CENDOTHERMI

Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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Practice problem


kJ6184

)(NO2)(O)NO(2 22

H

ggg

1146 kJmol

-157 x 10^4 kJ



molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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molkJH

OgHgOH

6483

)(2)(2 222









(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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(C) = m x (s)

tmsqtCq

cc

J

g

J g













qcal = -qrxn




he calorimeterTo do


Practice Question







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qcal = -qrxn




he calorimeterTo do


Practice Question







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he calorimeterTo do


Practice Question







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thermochemistry. energy - "the capacity to do work" unlike matter, energy is known and...

Documents

energy slide

constant energy

form of energy

forms of energy

conservation of energy

converted energy

energy closed systems

transfer of chemical