Heat Stoich.notebook
March 26, 2014
Heat Stoichiometry (yes, you can't escape it)
Some Background
Most stoichiometry problems will deal with a constant called enthalpy, H.
Enthalpy is the amount of heat used or released in a system.
Each chemical reaction has a H value.
If enthalpy is negative (initial energy greater than final), means system lost energy.
This is an ________________ reaction
If enthalpy is positive (final energy greater than initial), means system gained energy.
This is an ________________ reaction
Heat Stoich.notebook
March 26, 2014
Heat stoichiometry
This will call upon mass­mole and mole­mole stoichiometry, but will include enthalpy in the mix.
Example:
Need a balanced equation (aka thermochemical equation)
2 H2 (g) + O2 (g) => 2 H2O (g) H = ­241.83 kJ
(is this endothermic or exothermic?)
This means that for every 2 moles of hydrogen gas consumed, the heat of the reaction (aka enthalpy) is ­241.83 kJ.
Same goes for 1 mole of oxygen gas and 2 moles of water.
What if I wanted to find out how much heat is produced from the same reaction if 4 moles of H2 (g) is consumed?
Heat Stoich.notebook
March 26, 2014
Example:
H2O(l) + CO2(g) => C6H12O6(s) + O2(g) H=2808kJ
Is this reaction endothermic or exothermic?
How many grams of glucose would be produced from the reaction of 10.0 grams of water with excess carbon dioxide?
How many kJ of energy would be absorbed if 10.0 grams of water reacted with excess carbon dioxide? How many liters of carbon dioxide gas would need to react in order to absorb 5000 kJ of energy?
Example:
How many grams of Cl2 are needed to release a total of 1000 kJ of energy from this reaction?
P + Cl2 => PCl5 H = ­886 kJ