Heats of solutions Heats of solutions ((ΔΔH)H)
If given the choice, you’d prefer to If given the choice, you’d prefer to receive from that someone special:receive from that someone special:
A) A dozen red rosesA) A dozen red roses B) A dozen pink rosesB) A dozen pink roses C) A nice plantC) A nice plant D) A nice floral arrangementD) A nice floral arrangement
What is meant by the term heat of What is meant by the term heat of solution?solution?
It is the It is the netnet amount of amount of heat energy absorbed heat energy absorbed
or released when a or released when a solute dissolves in a solute dissolves in a
solvent.solvent.
What tends to be a confusing part of What tends to be a confusing part of this topic is the frame of reference. this topic is the frame of reference. The frame of reference we use is the The frame of reference we use is the “solution system” (the beaker where “solution system” (the beaker where
the solution is prepared).the solution is prepared).
So, if after dissolving solute in So, if after dissolving solute in solvent, the beaker/solution is solvent, the beaker/solution is
warmer than the surroundings, heat warmer than the surroundings, heat will flow:will flow:
A) In (into the beaker from the surroundings)A) In (into the beaker from the surroundings) B) Out (out of the beaker into the surroundings)B) Out (out of the beaker into the surroundings)
When the solution warms up due When the solution warms up due to the dissolving process, we say to the dissolving process, we say
the process is:the process is: A) Endothermic (meaning heat flows into A) Endothermic (meaning heat flows into
the beaker from the surroundings)the beaker from the surroundings) B) Exothermic (meaning heat flows out of B) Exothermic (meaning heat flows out of
the beaker into the surroundings)the beaker into the surroundings)
Because heat will flow out of a Because heat will flow out of a
warm beaker, we call that a –warm beaker, we call that a –ΔΔHH.. It is defined as negative because It is defined as negative because
energy is going out of the energy is going out of the solution system.solution system.
How do we explain How do we explain the temperature the temperature
change? (Why does change? (Why does the temperature the temperature
change?)change?)
It is a function of three types of It is a function of three types of intermolecular interactions. Identify intermolecular interactions. Identify
the three types.the three types.
They are:They are:
Solute-soluteSolute-solute SolventSolvent--solventsolvent
SolSoluteute--solsolventvent
Which one(s) absorb energy?Which one(s) absorb energy? 1) 1) Solute-soluteSolute-solute 2) Solvent2) Solvent--solventsolvent 3) 3) SolSoluteute--solsolventvent A) 1A) 1 B) 2B) 2 C) 3C) 3 D) 1 & 2D) 1 & 2
Energy is required to overcome Energy is required to overcome solute-solute solute-solute
and and solventsolvent--solventsolvent
interactions.interactions.
When new When new solute-solute-solventsolventinteractions are formed, energy is interactions are formed, energy is
released.released.
The difference between the The difference between the energy required (or absorbed) to energy required (or absorbed) to
overcome intermolecular overcome intermolecular attractions and the energy attractions and the energy
released in the new attractions released in the new attractions determines the net heat of determines the net heat of
solution.solution.
If during the dissolution, more If during the dissolution, more energy is released than required, energy is released than required,
the solution will feel:the solution will feel:
A) WarmerA) Warmer B) CoolerB) Cooler
If during the dissolution, more If during the dissolution, more energy is required than released energy is required than released
the solution is considered:the solution is considered:
A) EndothermicA) Endothermic B) ExothermicB) Exothermic
If during the dissolution, more If during the dissolution, more energy is required than released energy is required than released
the solution is defined to have a :the solution is defined to have a :
A) – A) – ΔΔH H B) + B) + ΔΔH H
If during the dissolution, more If during the dissolution, more energy is required than released energy is required than released
the solution will feel:the solution will feel:
A) WarmerA) Warmer B) CoolerB) Cooler
If during the dissolution, more If during the dissolution, more energy is released than required, energy is released than required,
the solution will feel:the solution will feel:
A) WarmerA) Warmer B) CoolerB) Cooler
If during the dissolution, more If during the dissolution, more energy is released than required energy is released than required
the solution is defined to have a :the solution is defined to have a :
A) – A) – ΔΔH H B) + B) + ΔΔH H
If during the dissolution, more If during the dissolution, more energy is released than required energy is released than required
the solution is considered:the solution is considered:
A) EndothermicA) Endothermic B) ExothermicB) Exothermic
If a solution has a – If a solution has a – ΔΔH, the solution H, the solution will feel _________ when the solute will feel _________ when the solute
is dissolved. is dissolved.
A) warm A) warm B) cool B) cool
If more energy is released than If more energy is released than required when a solute it dissolved, , required when a solute it dissolved, ,
the solution will feel _________ the solution will feel _________ when the solute is dissolved. when the solute is dissolved.
A) warm A) warm B) cool B) cool
If more energy is released than If more energy is released than required when a solute it dissolved, , required when a solute it dissolved, ,
the solution will have a: the solution will have a:
A) + A) + ΔΔH H
B) – B) – ΔΔH H
When NaOH is When NaOH is dissolved, the solution dissolved, the solution
gets warmergets warmer
When NaNOWhen NaNO33 is is
dissolved, the solution dissolved, the solution gets coolergets cooler
When a solution is When a solution is formed, an energy formed, an energy
change occurs.change occurs.
When a solution gets When a solution gets warmer, energy is warmer, energy is being ________.being ________.
released into the released into the surrounding surrounding environmentenvironment
Because the “solution Because the “solution system” is releasing system” is releasing
(losing) energy, (losing) energy, we’ll say it has a –we’ll say it has a –ΔΔH, H,
a negative heat of a negative heat of solution.solution.
When a solution gets When a solution gets cooler, energy is cooler, energy is being ________.being ________.
absorbed from the absorbed from the surrounding surrounding environmentenvironment
Because the “solution Because the “solution system” is absorbing system” is absorbing
(gaining) energy, (gaining) energy, we’ll say it has a +we’ll say it has a +ΔΔH, H,
a positive heat of a positive heat of solution.solution.
Where is this energy Where is this energy change coming from?change coming from?
Consider the large salt Consider the large salt block. If it is placed block. If it is placed in a pool after some in a pool after some time it will _______.time it will _______.
When it dissolves, When it dissolves, what was a large salt what was a large salt
block is now tiny block is now tiny particles spread particles spread
throughout the water. throughout the water.
In order to change it In order to change it from a block of salt into from a block of salt into many small particles of many small particles of salt energy is _______.salt energy is _______. A) RequiredA) Required B) ReleasedB) Released
So the act of breaking So the act of breaking apart the solute apart the solute
requires energy and requires energy and will cool the water. will cool the water.
There are also There are also attractions/bonds attractions/bonds between one water between one water particle and another particle and another
that need to be that need to be broken/overcome. broken/overcome.
Then there are Then there are attractions/bonds attractions/bonds between the solute between the solute
and solvent particles. and solvent particles. These release energy.These release energy.
It (heat of solution) is It (heat of solution) is measured in kJ/molmeasured in kJ/mol
Acid + carbonate Acid + carbonate
COCO22 + H + H22O + “salt”O + “salt”
NaNa22COCO33 + MgBr + MgBr22
2 NaBr + MgCO2 NaBr + MgCO33
No acid involved hereNo acid involved here
HAPPY HAPPY BIRTHDAY BIRTHDAY REANNA!!REANNA!!
From,From,
CaraCara
4 things “drive” a reaction4 things “drive” a reaction
Make a precipitate Make a precipitate (insoluble substance)(insoluble substance)
Make a gas Make a gas Make water (HMake water (H22O)O)
Movement of electronsMovement of electrons
Matter can be classified Matter can be classified into two categoriesinto two categories
Matter
MixturesPure
Substances
MixturesMixtures can be broken can be broken into two categoriesinto two categories
Mixtures
Homogeneous Heterogeneous
Pure SubstancePure Substance can be can be broken into two categoriesbroken into two categories
Pure Substances
Elements Compounds
““MatterMatter” can be classified two ” can be classified two waysways
Pure substancesPure substances ElementsElements CompoundsCompounds
MixturesMixtures Uniform mixtures are Uniform mixtures are
called…called… HomogenousHomogenous Non-uniform Non-uniform
mixtures are called…mixtures are called… HeterogeneousHeterogeneous
Chunky peanut butter would be Chunky peanut butter would be considered a ________ mixture.considered a ________ mixture.
HeterogeneousHeterogeneousWhy?Why?It isn’t “uniform”. It’s partly It isn’t “uniform”. It’s partly
creamy (peanut butter), and creamy (peanut butter), and partly chunky (peanuts)partly chunky (peanuts)
Chunky peanut butter would also Chunky peanut butter would also be considered a ________be considered a ________
Good snack right now Good snack right now Put it on some toastPut it on some toastMmmmMmmmYou’d probably want some You’d probably want some
milk too eh?milk too eh?
An exampleAn example
If something is If something is solublesoluble it it means that itmeans that it
Can be dissolvedCan be dissolved
““Dissolution” is just a fancy Dissolution” is just a fancy word meaningword meaning
DissolvesDissolves
If something If something cannotcannot be be dissolved we say that dissolved we say that
substance is…substance is…
InInsolublesoluble
In a solution of water and In a solution of water and sodium nitrate, the water is sodium nitrate, the water is
called the…called the…““SolventSolvent”” The The sodium nitratesodium nitrate is called the… is called the…
““Solute” (sol-yute)Solute” (sol-yute)(Or in Sam’s case: sol-hjute)(Or in Sam’s case: sol-hjute)
In a solution of water and salt, In a solution of water and salt, the salt is called the…the salt is called the…
““Solute” (sol-yute)Solute” (sol-yute)The water is called the…The water is called the…
““Solvent”Solvent”
In a mixture, the In a mixture, the substances that make up substances that make up the mixture the mixture retain their retain their individual propertiesindividual properties
When mixtures are made, When mixtures are made, the properties of the the properties of the
mixture are a mixture are a combination combination of the properties of what of the properties of what
makes up the mixturemakes up the mixture
We discussed three types We discussed three types of “mixtures”:of “mixtures”:
SolutionsSolutions
ColloidsColloids
SuspensionsSuspensions
Mixtures that are made up Mixtures that are made up of very small particles are of very small particles are
called…called…
“ “Solutions”Solutions”
A solution is made up A solution is made up of a solute and a of a solute and a
solventsolvent
There are a wide There are a wide range of range of
solute-solvent solute-solvent combinationscombinations
Types of Types of solutionsolution combinations: combinations: Gas-gasGas-gas Gas-liquidGas-liquid Liquid-gasLiquid-gas Liquid-liquidLiquid-liquid Liquid-solidLiquid-solid Solid-liquidSolid-liquid Solid-solidSolid-solid
A word about alcoholA word about alcohol
Not all alcohols are Not all alcohols are consumableconsumable
The alcohol from grain The alcohol from grain is “ethyl alcohol”. is “ethyl alcohol”.
This can be consumedThis can be consumed
The alcohol from The alcohol from wood is “methyl wood is “methyl
alcohol”. This cannot alcohol”. This cannot be consumed.be consumed.
Rubbing alcohol is Rubbing alcohol is “isopropyl alcohol”. “isopropyl alcohol”.
This cannot be This cannot be consumed.consumed.
A solution is a mixture A solution is a mixture of two different of two different
substances that are substances that are evenly distributedevenly distributed
Particle diagramsParticle diagrams
Mixtures made up of a Mixtures made up of a little larger particles are little larger particles are
called colloidal dispersionscalled colloidal dispersions
a.k.a colloidsa.k.a colloids Colloids scatter light Colloids scatter light
(Tyndall effect)(Tyndall effect)
A “colloidal dispersion” A “colloidal dispersion” is also called a colloidis also called a colloid
A colloid consists of a A colloid consists of a dispersed phasedispersed phase (what (what there is less of) and a there is less of) and a dispersing medium dispersing medium
(what there is more of)(what there is more of)
Colloids Colloids appear appear homogeneoushomogeneous but are but are
actually heterogeneousactually heterogeneous
Types of Types of colloidcolloid combinations: combinations:
Gas dispersed in a liquidGas dispersed in a liquid Liquid dispersed in a gasLiquid dispersed in a gas Liquid dispersed in a liquidLiquid dispersed in a liquid Liquid dispersed in a solidLiquid dispersed in a solid Solid dispersed in a liquidSolid dispersed in a liquid Solid dispersed in a gasSolid dispersed in a gas Solid network dispersed in a liquidSolid network dispersed in a liquid
Identify these types of Identify these types of colloidcolloid combinations:combinations:
ExampleExample Dispersed Dispersed phasephase
Dispersing Dispersing mediummedium
PaintPaint
SmokeSmoke
AerosolAerosol
JelloJello
Identify these types of Identify these types of colloidcolloid combinations:combinations:
ExampleExample Dispersed Dispersed phasephase
Dispersing Dispersing mediummedium
PaintPaint SolidSolid LiquidLiquid
SmokeSmoke SolidSolid GasGas
AerosolAerosol LiquidLiquid GasGas
JelloJello Solid networkSolid network liquidliquid
Identify these types of Identify these types of colloidcolloid combinations:combinations:
ExampleExample Dispersed Dispersed phasephase
Dispersing Dispersing mediummedium
ButterButter
Whipped creamWhipped cream
MilkMilk
Identify these types of Identify these types of colloidcolloid combinations:combinations:
ExampleExample Dispersed Dispersed phasephase
Dispersing Dispersing mediummedium
ButterButter LiquidLiquid SolidSolid
Whipped creamWhipped cream GasGas LiquidLiquid
MilkMilk LiquidLiquid LiquidLiquid
““suspensions” are…suspensions” are…
mixtures made up of mixtures made up of particles so large they must particles so large they must be stirred (agitated) to keep be stirred (agitated) to keep from falling to the bottomfrom falling to the bottom
A solution is made up of A solution is made up of particles that are very…particles that are very…
SmallSmall (less than 1 (less than 1 nanometer in size)nanometer in size)
Types of solute-solvent Types of solute-solvent combinationscombinations
If COIf CO22 is “dissolved in” O is “dissolved in” O2 2
this would be athis would be a
Gas solute (COGas solute (CO22) )
in a gas solvent (Oin a gas solvent (O22))
If COIf CO22 is dissolved in water is dissolved in water
this would be athis would be a
Gas solute (COGas solute (CO22) )
in a liquid solvent in a liquid solvent (water)(water)
If sugar is dissolved in If sugar is dissolved in waterwater this would be athis would be a
Solid solute (sugar) Solid solute (sugar) in a liquid solvent in a liquid solvent (water)(water)
If water is dissolved in airIf water is dissolved in air
this would be athis would be a
liquid solute (water) liquid solute (water) in a gas solvent (air) in a gas solvent (air)
If alcohol is dissolved in If alcohol is dissolved in waterwater this would be athis would be a
liquid solute (alcohol) liquid solute (alcohol) in a liquid solvent in a liquid solvent (water)(water)
An alloy is when two An alloy is when two metals are mixed. So this metals are mixed. So this
would be awould be asolid solute (tin) solid solute (tin) in a solid solvent in a solid solvent (copper) to make brass(copper) to make brass
Liquid solutions can be Liquid solutions can be classified as either classified as either
electrolytes or electrolytes or non-electrolytesnon-electrolytes
What does GatoradeWhat does Gatorade®® replenish?replenish?
ElectrolytesElectrolytesPrimarilyPrimarily Na Na++ and K and K++
““Electrolytes”Electrolytes” are substances which are substances whichDissolve in Dissolve in
waterwaterConduct Conduct
electricity electricity (current)(current)
““Non-electrolytes”Non-electrolytes” are substances are substances whichwhich
Dissolve in Dissolve in waterwater
Do not Do not conduct conduct electricity electricity (current)(current)
Electrolytes conduct electricity Electrolytes conduct electricity becausebecause
They form They form ionsions in water in water Examples:Examples: NaCl NaCl Na Na++ + Cl + Cl--
NaOH NaOH Na Na++ + OH + OH--
KK22SOSO44 2 K 2 K++ + SO + SO44--
Electrolytes conduct electricity Electrolytes conduct electricity becausebecause
They form They form ionsions in water in waterAnother word for this is they Another word for this is they
““dissociatedissociate”.”.
What does GatoradeWhat does Gatorade®® replenish?replenish?
ElectrolytesElectrolytesPrimarilyPrimarily Na Na++ and K and K++
Where do these sodium and Where do these sodium and potassium ions come from?potassium ions come from?
Sodium comes from NaClSodium comes from NaCl NaCl NaCl Na Na++ + Cl + Cl-- KK+ + comes from KHcomes from KH22POPO44
KHKH22POPO44 K K+++ H+ H22POPO44--
What really happens What really happens when a chemical when a chemical
dissolves in a liquid?dissolves in a liquid? Water molecules Water molecules surroundsurround
molecules of the solute molecules of the solute chemicalchemical
This process of the This process of the solvent breaking apart solvent breaking apart and surrounding the and surrounding the
solute is called solute is called “solvating”“solvating”
RatesRates of dissolution of dissolution(dissolving)(dissolving)
How fast something How fast something dissolvesdissolves
Three things can be done to make Three things can be done to make most solids dissolve faster:most solids dissolve faster:
Stir it (agitate)Stir it (agitate)Increase the surface area Increase the surface area
(make the particles smaller)(make the particles smaller)Heat up the solutionHeat up the solution
Why do each of these help to Why do each of these help to solvate the solute?solvate the solute?
They make the collisions They make the collisions between the solute and between the solute and solvent more frequent.solvent more frequent.
(i.e., bring fresh solvent into (i.e., bring fresh solvent into contact with the solute)contact with the solute)
Electrolytes conduct electricity Electrolytes conduct electricity becausebecause
They form They form ionsions in water in waterAnother word for this is they:Another word for this is they: “ “dissociatedissociate”.”.
What does KNOWhat does KNO33
dissociate into?dissociate into?
KK++ and NO and NO33--
What does KWhat does K22SOSO44
dissociate into?dissociate into?
2K2K++ and SO and SO4422--
What does Mg(OH)What does Mg(OH)22
dissociate into?dissociate into?
MgMg2+2+ and 2 OH and 2 OH--
Solutions that cannot hold Solutions that cannot hold any more solute are any more solute are
called…called…
“ “saturated” solutions”saturated” solutions”
Saturated solutions are in Saturated solutions are in equilibrium becauseequilibrium because
If some undissolved solute If some undissolved solute dissolves, then some already dissolves, then some already dissolved solute will dissolved solute will recrystalize. These processes recrystalize. These processes happen at the happen at the same same raterate..
Solutions that can hold Solutions that can hold more solute than they more solute than they
presently have are called…presently have are called…
““unsaturated” solutionsunsaturated” solutions
A “super-saturated” solution is A “super-saturated” solution is one that one that
Has dissolved more solute Has dissolved more solute than a similar solution would than a similar solution would under normal conditions.under normal conditions.
(They are very unstable) (They are very unstable)
A “super-saturated” solution is A “super-saturated” solution is made bymade by
Heating the solution up so Heating the solution up so you can get more solute to you can get more solute to dissolve in it, then letting it dissolve in it, then letting it cool.cool.
Molarity (M)Molarity (M) is a measure is a measure of a solution’s…of a solution’s…
ConcentrationConcentration
Which is more concentrated, a Which is more concentrated, a 1.40 M NaOH solution, or a 1.40 M NaOH solution, or a
0.55 M Na0.55 M Na22SOSO44 solution? solution?
The 1.40 M NaOH The 1.40 M NaOH solutionsolution
The formula for The formula for calculating Molarity (M)calculating Molarity (M)
is:is:
Moles of solute Liters of solution
Solubility of Solubility of gases gases as as it relates toit relates to pressure pressure
How is soda pop carbonated?How is soda pop carbonated?(How do they get the CO(How do they get the CO22 gas gas
in it?)in it?)They force it in by bottling it at They force it in by bottling it at
high pressurehigh pressure (5-10 (5-10 atmospheres of pressure) atmospheres of pressure)
So we can say that as the So we can say that as the pressure of a gas above the pressure of a gas above the
solution increases, the solubility solution increases, the solubility of the gas…of the gas…
IncreasesIncreases(more pressure means more gas (more pressure means more gas
will dissolve)will dissolve)This is known as…(whose law?) This is known as…(whose law?) ““Henry’s Law”Henry’s Law”
Gas solubility as it relates Gas solubility as it relates to to temperaturetemperature
Two cans of pop are opened. Two cans of pop are opened. One is placed in the One is placed in the fridgefridge;;
one is placed on the one is placed on the countercounter. .
Which can “goes flat” sooner Which can “goes flat” sooner and why?and why?
The one on the counter The one on the counter because the warmer the because the warmer the pop, the quicker it loses pop, the quicker it loses
it’s fizz (COit’s fizz (CO22 gas) gas)
So, as the So, as the temperaturetemperature of a of a solution goes up, the solution goes up, the
solubility of a gassolubility of a gas in that in that solution goes…solution goes…
Down. Down. Less gas will dissolve Less gas will dissolve in a warm solution than in a in a warm solution than in a cold solution.cold solution.
Ions that do not participate in a Ions that do not participate in a chemical reaction are called…chemical reaction are called…
Spectator ionsSpectator ions
A colligative property on one that A colligative property on one that depends on the _________, not depends on the _________, not
the _________the _________ConcentrationConcentrationNot the identity (so it makes Not the identity (so it makes
no difference if we’re talking no difference if we’re talking about sugar, salt, lithium about sugar, salt, lithium bromide….bromide….
A colligative property on one that A colligative property on one that depends on the _________, not depends on the _________, not
the _________the _________ConcentrationConcentrationNot the identity (so it makes Not the identity (so it makes
no difference if we’re talking no difference if we’re talking about sugar, salt, lithium about sugar, salt, lithium bromide….bromide….