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3 cards from this section. Quick, good the night before a test.
What does Hess's Law state?
Remember, it's based on the initial and final states of a reaction.
Define a state function.
Temperature and pressure are examples of state functions.
What does Hess's Law state?
Focus on what connects path and enthalpy.
If a reaction A → B has a positive enthalpy change, what does it indicate?
Think about whether the energy is gained or lost.
Consider the following reaction steps: Step 1: C(graphite) + O2(g) → CO2(g) with dH = -393.5 kJ; Step 2: CO(g) + 1/2 O2(g) → CO2(g) with dH = -283 kJ. Given C(graphite) → CO(g) shows dH, calculate the enthalpy change for this step.
Remember to rearrange the steps accordingly.
Using Hess's law, predict the enthalpy change for the reaction where H2(g) + 1/2O2(g) → H2O(l) is known to release 285.8 kJ, and find the enthalpy of formation for H2O(l).
Think about how combustion reactions relate to formation reactions.
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