Bellwork‐Hotwater

1.Whyissteampoten7allymoredangerousthanhotwater?

2.Which has a higherspecific heat, water orsand?

Explain using examples

BUTSTEAMCANBURNLIKEFIREWITHANEXTRA40.67kJ/molOFENERGY.ANDitisoEenhoIerthan100°C

Let’sfillinthechartonyourhomework!

Bellwork‐Endoorexo2

Arethefollowingprocessesendothermicorexothermic?

1.Burningwood2.Boilingwater3.Diges7ngsugar4.Mixingtwoaqueoussolu7ons,thecombina7ongetscold.

5.ΔH=‐380kJ/mol6.Egg+heatover‐easy

Athermochemicalequa7ontellsustheamountofenergythatisexchangedduringtheprocess

C3H8(g)+O2(g)CO2(g)+H2O(g)ΔH=‐2220kJ

2NaHCO3(s)Na2CO3(s)+H2O(g)+CO2(g)ΔH=129kJ

C3H8(g)+O2(g)CO2(g)+H2O(g)ΔH=‐2220kJ

C3H8(g)+O2(g)CO2(g)+H2O(g)+2220kJ

2NaHCO3(s)Na2CO3(s)+H2O(g)+CO2(g)ΔH=129kJ

129kJ+2NaHCO3(s)Na2CO3(s)+H2O(g)+CO2(g)

TheycanbewriYenintwoways

C3H8(g)+O2(g)CO2(g)+H2O(g)ΔH=‐2220kJ

2220kJofenergyareproducedforeverymoleofC3H8(g)thatisburned.

5molesx‐2220kJ/mole=‐11,100kJ

Howmuchenergyisproducedby5moles?

2NaHCO3(s)Na2CO3(s)+H2O(g)+CO2(g)ΔH=129kJ

129kJisabsorbedbyevery2molesofNaHCO3(s)thatisdecomposed.

Whatistheenergychange(ΔH)forthedecomposi7onof25gofNaHCO3(s)?

25gx1mole84g

=.298moles 129kJ2molx =19.22kJ

Sec7on17.4‐HonorsonlyCalcula7ngHeatsofReac7on

Emeraldsarecomposedoftheelementschromium,aluminum,silicon,oxygen,andberyllium.

Whatifyouwantedtodeterminetheheatofreac7onwithoutactuallybreakingthegemsdowntotheircomponentelements?

Hess’slawallowsyoutodeterminetheheatofreacVonindirectly.

Hess’slawofheatsumma7onstatesthatifyouaddtwoormorethermochemicalequa7onstogiveafinalequa7on,thenyoucanalsoaddtheheatsofreac7ontogivethefinalheatofreac7on.

Manipulate the given equations toobtain the “equation of interest”.

change sign of∆H

switchingreactants &products

Flip reactions

Multiply ∆H bysame number

Multiply allcoefficientsby the samenumber

Multiplyreactions

Add ∆H valuesA →BPlus C→DGivesA+C →B+D

Add reactions

BUT YOU MUSTBYYOU CAN

StandardHeatsofForma7onForareac7onthatoccursatstandardcondi7ons,youcancalculatetheheatofreac7onbyusingstandardheatsofforma7on.

17.4

Thestandardheatofforma7on(∆Hf°)ofacompoundisthechangeinenthalpythataccompaniestheforma7onofonemoleofthecompoundfromitselementswithallsubstancesintheirstandardstatesat25°C.

17.4

17.4

TheStandardHeatofForma7onofWater

17.4

StandardHeatsofFormaVon17.4