more heat calculations what have we done?. we can figure out heat values and then put them into kj /...

More Heat Calculations What have we done?

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More Heat Calculations

What have we done?

We can figure out heat values and then put them into kJ / mole

What have we done?

We can figure out heat values and then put them into kJ / mole

We can put heat on the correct side of the equation and then do STOICH!

What have we done?

We can figure out heat values and then put them into kJ / mole

We can put heat on the correct side of the equation and then do STOICH!

Hess’s Law problems

What have we done?

We can figure out heat values and then put them into kJ / moleWe can put heat on the correct side of the equation and then do STOICH!Hess’s Law problemsNow, let’s calculate heat by just having the equation

Heat of formation

CH4(g) + 2O2(g) ==> CO2(g) + 2H2O (g)

H = ?

Find the Standard Heat of Formation for each substance. Hºf

Page 7: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Hºf how it exists at 1 atm and 25ºC.

Page 8: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Hºf --> how it exist at 1 atm and 25 °C.

Get used to seeing °

Page 9: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Hºf how it exist at 1 atm and 25ºC.

Get used to seeing °

For elements and diatomics molecules Hºf = 0

Page 10: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Hºf --> how it exists at 1 atm and 25ºC.

Get used to seeing °

For elements and diatomics molecules

Hºf=0

The rest - Look at Appendix

Page 11: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Hºf --> how it exists at 1 atm and 25 ºC.

Get used to seeing °

For elements and diatomics molecules

Hºf = 0

The rest - Look at Appendix

Coefficients act as multipliers. WHY? Look at units.

Page 12: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Hºf --> how it exists at 1 atm and 25 ºC.

Get used to seeing °

For elements and diatomics molecules Hºf = 0

The rest - Look at Appendix 4 page A21

Coefficients act as multipliers. WHY? Look at units.

Always! H = ∑P - ∑R ∑=sum

Page 13: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Remember! Hºf is the change in enthalpy that accompanies the formation of 1 mole of a compound from its elements.

Therefore: In order to find the Hºf of a compound, you need to break it up into individual elements!

Ca(s) + S(s) + 2O2(g) CaSO4(s)

Page 14: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

CH4(g) + 2O2(g) ==> CO2(g) + 2H2O(g)

H = ?

Look up values. Make sure you have correct states of matter.

Page 15: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

CH4(g) + 2O2(g) ==> C02(g) + 2H20(l)

H = ?

((-75 kJ) + 2(0kJ)) ==> ((-393.5kJ) + 2(-242kJ))

Page 16: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

CH4(g) + 2O2(g) ==> C02(g) + 2H20(l)

H = ?((-75 kJ) + 2(0kJ)) ==> ((-393.5kJ) + 2(-242kJ))

-75 kJ ==> -393.5 kJ + -484kJ

-877.5 kJ

Page 17: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

CH4(g) + 2O2(g) ==> C02(g) + 2H20g)

H = ?((-75 kJ) + 2(0kJ)) ==> ((-393.5kJ) + 2(-242kJ))

-75 kJ ==> -393.5 kJ + -484 kJ

-877.5 kJ

H = -877.5 kJ - (-75 kJ)

H = -802.5 kJ

Page 18: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

Hºf

Problems

Calculate the standard change in enthalpy for the following reaction.

2 Al(s) + Fe203(s) Al203(s) + 2 Fe(s)

Page 19: More Heat Calculations What have we done?. We can figure out heat values and then put them into kJ / mole

One More

2) Students tend not to like this format!

a) Write the combustion reaction for methanol.

b) For the combustion of methanol, H, is equal to -1454 kJ. Find the heat of formation of methanol given only the information below. H°f for CO2 (g) = -393.5 kJ/mole

H°f for H2O (g) = -242 kJ/mole

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