CH 15 Calculating Enthalpy Changes

Question 1

Why is it sometimes impossible or impractical to measure the enthalpy of a reaction by using a calorimeter

Answer 1

• The reaction occurs so slowly that measuring the enthalpy change is impossible
• Some reactions occur under conditions that are difficult to duplicate in a laboratory
• Some reactions produce products other than the desired ones

Question 2

Hess’s Law

Answer 2

States that if you can add two or more thermochemical equations to produce a final equation for reaction, than the sum of the enthalpy changes for the individual reactions is the enthalpy change for the final reaction

Question 3

Standard enthalpy of formation

Answer 3

The change in enthalpy that accompanies the formation of one more of the compound in a standard state from its elements in their standard states.