Given the following thermochemical equation, calculate the heat (in kJ) involved in decomposing 18.0 g of
water to give one mole of H2 (g).
You do not provide the thermochemical formation or the heat of reaction. It should have been part of your problem statement.
18.0 g of H2O is one mole. The answer will be the heat of formation of H2O, expressed as Kcal or kJ per mole. The decomposition reaction is endothermic.
My textbook says the heat of formation of H2O is -57.8 kcal/mol. The minus sign means the formation of H2O from H2 and O2 is exothermic. For your answer, forget the minus sign and you will have the heat required to decompose.
Since that want it in kJ, you will have to multiply by 4.18 kJ/kcal
The specific heat of aluminum is 0.0215 cal/g °C. If a 4.55 g sample of
aluminum absorbs 2.55 cal of energy, by how much will the temperature of
the sample change?
0.249
26.1
To calculate the heat involved in decomposing water to give one mole of hydrogen gas (H2), we need to follow these steps:
1. Start by writing out the balanced thermochemical equation for the decomposition of water. The equation is:
2H2O(l) -> 2H2(g) + O2(g)
This equation tells us that two moles of water decompose to form two moles of hydrogen gas and one mole of oxygen gas.
2. Determine the molar mass of water (H2O) and hydrogen gas (H2). The molar mass of water is the sum of the atomic masses of hydrogen (H) and oxygen (O), which are 1.008 g/mol and 16.00 g/mol respectively. So, the molar mass of water is 18.016 g/mol. The molar mass of hydrogen gas is simply 2.016 g/mol, since it consists of 2 hydrogen atoms.
3. Convert the given mass of water (18.0 g) to moles. We can use the molar mass of water to convert the mass to moles:
moles of water = mass / molar mass
moles of water = 18.0 g / 18.016 g/mol
moles of water = 0.999 mol (approximately)
Here, we have obtained approximately 1 mole of water.
4. Use the stoichiometric ratio from the balanced equation to determine the number of moles of hydrogen gas produced. The equation tells us that for every 2 moles of water decomposed, 2 moles of hydrogen gas are produced. Since we have 1 mole of water, we will get 1 mole of hydrogen gas.
5. Calculate the heat involved in the decomposition of the given amount of water to give one mole of hydrogen gas. The heat change is equal to the heat of formation of the products minus the heat of formation of the reactants. The heat of formation of H2O(l) is -285.8 kJ/mol (negative because it is an exothermic process), and the heat of formation of H2(g) is 0 kJ/mol. Therefore,
heat change = heat of formation of products - heat of formation of reactants
heat change = 0 kJ/mol - (-285.8 kJ/mol)
heat change = 285.8 kJ/mol
So, the heat involved in decomposing 18.0 g of water to give one mole of H2(g) is 285.8 kJ.