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More Heat Calculations. What have we done?. 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!.

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## More Heat Calculations

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**More Heat Calculations**What have we done?**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 / mole • We can put heat on the correct side of the equation and then do STOICH! • Hess’s Law problems • Now, 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**Hºf**• Hºf how it exists at 1 atm and 25ºC.**Hºf**• Hºf --> how it exist at 1 atm and 25 °C. • Get used to seeing °**Hºf**• Hºf how it exist at 1 atm and 25ºC. • Get used to seeing ° • For elements and diatomics molecules Hºf = 0**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**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.**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**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)**Hºf**CH4(g) + 2O2(g) ==> CO2(g) + 2H2O(g) H = ? Look up values. Make sure you have correct states of matter.**Hºf**CH4(g) + 2O2(g) ==> C02(g) + 2H20(l) H = ? ((-75 kJ) + 2(0kJ)) ==> ((-393.5kJ) + 2(-242kJ))**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**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**Hºf**Problems Calculate the standard change in enthalpy for the following reaction. • 2 Al(s) + Fe203(s) Al203(s) + 2 Fe(s)**One More**• 2) Students tend not to like this format! a) Write the combustion reaction for methanol. • 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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