What energy change is associated with the reaction to obtain one mole of H2 from one mole of water vapor? The balanced equation is 2 H2O(g) -> 2 H2(g) + O2(g)and the relevant bond energies are
H-H : 436 kJ/mol; H-O : 467 kJ/mol;
O-O : 146 kJ/mol; O=O : 498 kJ/mol.
1. +249 kJ
2. −436 kJ
3. +425 kJ
4. −425 kJ
2 H2O(g) -> 2 H2(g) + O2(g)
H2O(g) -> H2(g) + 1/2 O2(g)
1mol 1 mol 1/2 mole
each mole H2O has 2 moles of O-H bonds to break (energy requiring) = 2 x 467 = 934 kJ
Each mole H2 has 1 mole H-H bonds to make (energy releasing) = 436 kJ
Each mole O2 has 1 mole O=O bonds to make. So 1/2 mole = 1/2 x 498 = 249 kJ
Energy required in bond breaking = 934 kJ
Energy released in bond making = 436 + 249 = 685 kJ
Balance needed = 934 - 685 = 249 kJ
So Delta H = +249kJ
To determine the energy change associated with the reaction, we need to calculate the energy required to break the bonds in water vapor and the energy released when the new bonds form in H2 and O2.
The bonds that need to be broken in water vapor are two O-H bonds, with a bond energy of 467 kJ/mol each. So the total energy required to break the bonds in one mole of water vapor is (2 O-H bonds) * (467 kJ/mol) = 934 kJ.
Next, we need to calculate the energy released when the new bonds form in H2 and O2. There are four H-H bonds formed, each with a bond energy of 436 kJ/mol. So the total energy released during the formation of H2 is (4 H-H bonds) * (436 kJ/mol) = 1744 kJ.
There is one O=O bond formed in the reaction, with a bond energy of 498 kJ/mol. So the total energy released during the formation of O2 is (1 O=O bond) * (498 kJ/mol) = 498 kJ.
Now, we can calculate the overall energy change by summing up the energy required to break the bonds in water vapor and the energy released during the formation of H2 and O2:
Energy Change = (Energy required to break bonds) - (Energy released during formation)
Energy Change = 934 kJ - (1744 kJ + 498 kJ)
Energy Change = 934 kJ - 2242 kJ
Energy Change = -1308 kJ
Therefore, the energy change associated with the reaction to obtain one mole of H2 from one mole of water vapor is -1308 kJ, which is equivalent to option 4. -425 kJ.
To determine the energy change associated with the reaction, we need to calculate the energy required to break the bonds in the reactants and the energy released when the bonds are formed in the products.
Let's start by calculating the energy required to break the bonds in water (H2O). The balanced equation tells us that we need two moles of water (2 H2O) to obtain two moles of hydrogen gas (2 H2) and one mole of oxygen gas (O2).
The bond energy required to break the H-O bonds in two moles of water is:
2 mol x 2 H-O bonds x 467 kJ/mol = 1868 kJ
The bond energy required to break the O-O bond in one mole of oxygen gas is:
1 mol x 1 O-O bond x 146 kJ/mol = 146 kJ
So, the total energy required to break the bonds in the reactants is:
1868 kJ + 146 kJ = 2014 kJ
Next, let's calculate the energy released when the bonds are formed in the products. The balanced equation tells us that two moles of hydrogen gas (2 H2) are formed.
The bond energy released when the H-H bond is formed in two moles of hydrogen gas is:
2 mol x 1 H-H bond x 436 kJ/mol = 872 kJ
Therefore, the energy change associated with the reaction is the difference between the energy required to break the bonds in the reactants and the energy released when the bonds are formed in the products:
Energy change = Energy required to break bonds - Energy released when bonds are formed
Energy change = 2014 kJ - 872 kJ = 1142 kJ
The energy change is positive, indicating that energy is absorbed in this reaction. Therefore, the correct answer is 1. +249 kJ.