DETERMINE the enthalpy for the reaction CH4(g)+NH3(g)->HCN(g)+3H2(g)
Look up delta Hfo and
delta Hrxn = (n*sum delta H products)-(n*sum delta H reactants).
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To determine the enthalpy for the reaction CH4(g) + NH3(g) -> HCN(g) + 3H2(g), you will need to find the enthalpies of formation for each compound involved in the reaction and use them to calculate the overall enthalpy change.
The enthalpy of formation (ΔHf) is the enthalpy change associated with the formation of one mole of a compound from its constituent elements, all in their standard states.
The ΔHf values you will need for this reaction are as follows:
ΔHf(CH4) = -74.8 kJ/mol
ΔHf(NH3) = -46.1 kJ/mol
ΔHf(HCN) = 135.1 kJ/mol
ΔHf(H2) = 0 kJ/mol (since it is an elemental form)
Now, you can calculate the overall enthalpy change (ΔH) using the equation:
ΔH = Σ ΔHf(products) - Σ ΔHf(reactants)
Where Σ ΔHf(products) is the sum of the ΔHf values for the products, and Σ ΔHf(reactants) is the sum of the ΔHf values for the reactants.
In this case, the equation becomes:
ΔH = ΔHf(HCN) + 3ΔHf(H2) - ΔHf(CH4) - ΔHf(NH3)
Plugging in the values:
ΔH = 135.1 kJ/mol + 3(0 kJ/mol) - (-74.8 kJ/mol) - (-46.1 kJ/mol)
Simplifying:
ΔH = 135.1 kJ/mol + 0 kJ/mol + 74.8 kJ/mol - (-46.1 kJ/mol)
ΔH = 256 kJ/mol
So, the enthalpy change for the reaction CH4(g) + NH3(g) -> HCN(g) + 3H2(g) is +256 kJ/mol.
To determine the enthalpy change (ΔH) for a reaction, you will need the enthalpy values of the individual substances involved in the reaction. In this case, you want to find the enthalpy change for the reaction:
CH4(g) + NH3(g) -> HCN(g) + 3H2(g)
The enthalpy change can be calculated using the equation:
ΔH = ΣΔH(products) - ΣΔH(reactants)
where ΣΔH represents the sum of the enthalpy values of each compound.
To determine the enthalpy values for each substance, you have a few options:
Option 1: Experimental Data
You can search for experimental data or use tables that provide enthalpy values of each compound. These values are typically given in units of kJ/mol.
Option 2: Hess's Law
If you can't find the enthalpy values directly, you can use Hess's law. This law states that the enthalpy change of a reaction is independent of the reaction pathway and depends only on the initial and final states of the system.
For example, instead of finding the enthalpy change for CH4(g) + NH3(g) -> HCN(g) + 3H2(g), you can break it down into two steps:
Step 1: CH4(g) -> C(g) + 4H(g)
Step 2: C(g) + 4H(g) + NH3(g) -> HCN(g) + 3H2(g)
Now you can find the enthalpy change for each step separately, either through experimental data or available enthalpy values.
Once you have the enthalpy values for each step, you can sum them up to obtain the overall enthalpy change for the reaction.
Note: Make sure the enthalpy values you use are at the same temperature and pressure as the reaction you are studying.
By following one of these methods, you should be able to determine the enthalpy change for the reaction CH4(g) + NH3(g) -> HCN(g) + 3H2(g).