Consider the following chemical reaction:
2H2O2(L) �¨ 2H2O(L) + O2(g) ƒ¢Hrxn = -196.1 kJ
How much heat is released if 2 moles of O2 are produced?
Would you believe twice as much as from one mol (and 1 mol is 196.1 kJ IF that is 196.1 kJ for the reaction as written)?
The given reaction shows that for every 2 moles of H2O2, 1 mole of O2 is produced. Therefore, if 2 moles of O2 are produced, we can calculate how much H2O2 is needed using the mole ratio:
1 mole O2 is produced from 2 moles H2O2
So, to produce 2 moles O2, we need (2/1) x 2 = 4 moles of H2O2.
Since the enthalpy change of the reaction is given as -196.1 kJ, we can use this value to calculate the amount of heat released when 2 moles of O2 are produced.
The enthalpy change per mole of O2 produced can be calculated using the equation:
ΔHrxn = q/n
Where:
ΔHrxn = enthalpy change
q = heat released or absorbed
n = number of moles
Rearranging the equation to solve for q, we have:
q = ΔHrxn x n
Substituting the given values:
q = -196.1 kJ x 2 moles
q = -392.2 kJ
Therefore, when 2 moles of O2 are produced, 392.2 kJ of heat is released.
To calculate the amount of heat released if 2 moles of O2 are produced, we need to use the given value of the enthalpy change of the reaction (∆Hrxn) and the stoichiometry of the reaction.
The stoichiometry of the reaction states that for every 2 moles of H2O2 reacting, 1 mole of O2 is produced.
Given:
∆Hrxn = -196.1 kJ
Number of moles of O2 produced = 2
To calculate the amount of heat released, we need to find the moles of H2O2 that reacts to produce the given number of moles of O2. Since we know the stoichiometry of the reaction, we can set up a proportion:
2 moles of H2O2 / 1 mole of O2 = x moles of H2O2 / 2 moles of O2
Solving for x, we get:
x = (2 moles of H2O2 / 1 mole of O2) * (2 moles of O2 / 1 mole of H2O2)
x = 4 moles of H2O2
Now that we know the moles of H2O2 reacting, we can calculate the amount of heat released using the equation:
q = ∆Hrxn * (moles of H2O2 reacting / stoichiometric coefficient of H2O2)
q = -196.1 kJ * (4 moles of H2O2 / 2 moles of H2O2)
q = -196.1 kJ * 2
q = -392.2 kJ
Therefore, if 2 moles of O2 are produced, the amount of heat released is -392.2 kJ. The negative sign indicates that the reaction is exothermic.