How do you calculate deltaHf using the # of moles from a balanced equation?
How do you connect the Law of Conservation of Energy to a Thermochemical Equation?
Thanks so much!
It would be so much easier to explain if you had a problem.
Ok, well it gives us the equation:
CH4 + 2O2 --> CO2 + 2H20 ( I balanced it)
And then it asks us to calculate: deltaHf (#of mol) I think we have to do that using the mole ratio and the balanced equation?
Sorry if it's confusing :/
It's done this way; you need to look up the dHf values(heat formation) in tables which usually can be found in your text.
dHrxn = (n*dHf products) - (n*dH reactants)
To calculate the enthalpy change of formation (ΔHf) using the number of moles from a balanced equation, you need to follow these steps:
1. Start with a balanced chemical equation representing the formation reaction of the compound you are interested in.
2. Determine the stoichiometric coefficients (molar ratios) of the reactants and products in the balanced equation.
3. Find the enthalpy change (ΔH) for each compound in the reaction. This information is usually given or can be found in thermodynamic tables.
4. Multiply the ΔH value for each compound by the corresponding stoichiometric coefficient from the balanced equation.
5. Add up all the individual ΔH values calculated in the previous step to obtain the ΔHf of the compound.
For example, let's consider the formation of water (H2O) from its elements hydrogen (H2) and oxygen (O2):
The balanced equation is:
2 H2(g) + O2(g) → 2 H2O(l)
Given the enthalpy change values:
ΔH(H2) = 0 kJ/mol (since it's the standard state)
ΔH(O2) = 0 kJ/mol (since it's the standard state)
ΔH(H2O) = -286 kJ/mol (formation of liquid water)
Using the stoichiometric coefficients, we can calculate ΔHf for water:
ΔHf(H2O) = (2 moles of H2) * (0 kJ/mol H2) + (1 mole of O2) * (0 kJ/mol O2) + (2 moles of H2O) * (-286 kJ/mol H2O)
= 0 kJ/mol + 0 kJ/mol + (-572 kJ/mol)
= -572 kJ/mol
Thus, the enthalpy change of formation (ΔHf) for water is -572 kJ/mol.
Now let's address your second question about connecting the Law of Conservation of Energy to a Thermochemical Equation:
The Law of Conservation of Energy states that energy cannot be created or destroyed; it can only be transferred or transformed from one form to another. In the context of thermochemical equations, this law applies to the enthalpy change (ΔH) that occurs during a chemical reaction.
A thermochemical equation represents a chemical reaction along with the associated enthalpy change. It typically includes the reactants, products, stoichiometric coefficients, and the value of ΔH. The value of ΔH indicates the energy absorbed or released during the reaction.
The Law of Conservation of Energy is connected to a thermochemical equation by ensuring that the energy on both sides of the equation remains balanced. The total energy absorbed or released during the reaction (as indicated by ΔH) must equal the total energy required or produced by the reactants and products.
In other words, the enthalpy change on the left side of the equation must be equal to the enthalpy change on the right side. This connection ensures that energy is conserved throughout the reaction, complying with the Law of Conservation of Energy.
By using thermochemical equations and considering the enthalpy changes associated with the reactants and products, we can quantitatively analyze and understand the energy flow in chemical reactions.