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What are the general steps to solve a Hess's Law problem?
1. Identify target equation. 2. Manipulate given equations (reverse, multiply) to match target. 3. Add manipulated equations and their ΔH values.
What happens to ΔH when reversing a reaction in Hess's Law?
The sign of ΔH is changed (positive becomes negative, and vice versa).
What happens to ΔH when multiplying a reaction by a coefficient in Hess's Law?
ΔH is also multiplied by the same coefficient.
What do you do with the ΔH values after manipulating the equations?
Add all the manipulated ΔH values together to obtain the overall ΔH for the target reaction.
What should be done after manipulating the equations and adding them together?
Cancel out any spectator species that appear on both sides of the equation to obtain the final target equation.
Define 'state function'.
A property whose value does not depend on the path taken to reach a specific state, only on the initial and final states.
What does 'pathway dependent' mean?
A process or function that depends on the specific route taken. The result changes if a different path is taken.
What does 'pathway independent' mean?
A process or function that does not depend on the specific route taken. The result is the same no matter which path you choose.
Define enthalpy (H).
A thermodynamic property of a system that is the sum of the internal energy of the system plus the product of pressure and volume.
Define Hess's Law.
The enthalpy change for a reaction is independent of the path taken; it's a state function.
What is the effect of reversing a reaction on the sign of ΔH?
Reversing a reaction changes the sign of ΔH (positive becomes negative, and vice versa).
What is the effect of multiplying a reaction by a factor 'n' on the value of ΔH?
ΔH is also multiplied by the same factor 'n'.
What is the result of adding multiple reactions together in Hess's Law?
The corresponding ΔH values are added together to give the overall ΔH for the net reaction.
What happens if you forget to change the sign of ΔH when reversing a reaction?
The calculated enthalpy change for the overall reaction will be incorrect.
What happens if the final equation does not match the target equation when using Hess's Law?
The calculated enthalpy change will be incorrect, indicating an error in the manipulation or cancellation of species.