AP Chemistry · Unit 6: Thermochemistry
6.9 Hess’s Law
In short
You are expected to understand that chemical and physical processes can be broken down into a series of steps, each with its own energy change.
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What else do you need to know about Hess’s Law?
You must apply the principles of Hess's law to determine the overall enthalpy change of a process: reversing a reaction reverses the sign of the enthalpy change, multiplying a reaction by a factor multiplies the enthalpy change by the same factor, and adding reactions requires adding their individual enthalpy changes. The concept of state functions is explicitly excluded and will not be assessed on the AP Exam.
How is Hess’s Law tested on the exam?
You are assessed on your ability to identify quantities needed to solve a problem from given information (e.g., text, mathematical expressions, graphs, or tables). You may be required to manipulate a given set of chemical equations (reversing, multiplying by coefficients) and their corresponding enthalpy changes to calculate the net enthalpy change for an overall reaction.
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Hess’s Law: common questions
What do you need to know about Hess’s Law for AP Chemistry?
You are expected to understand that chemical and physical processes can be broken down into a series of steps, each with its own energy change.
How is Hess’s Law tested on the AP Chemistry exam?
You are assessed on your ability to identify quantities needed to solve a problem from given information (e.g., text, mathematical expressions, graphs, or tables). You may be required to manipulate a given set of chemical equations (reversing, multiplying by coefficients) and their corresponding enthalpy changes to calculate the net enthalpy change for an overall reaction.
Where does Hess’s Law fit in AP Chemistry?
Hess’s Law is topic 6.9 in Unit 6: Thermochemistry of AP Chemistry.
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