UNITS 5&15- ENERGETICS AND THERMOCHEMISTRY

ESSENTIAL IDEAS

• In chemical transformations energy can neither be created nor destroyed (the first law of thermodynamics).
• The enthalpy changes from chemical reactions can be calculated from their effect on the temperature of their surroundings.
• Energy is absorbed when bonds are broken and is released when bonds are formed.
• The concept of the energy change in a single step reaction being equivalent to the summation of smaller steps can be applied to changes involving ionic compounds.
• A reaction is spontaneous if the overall transformation leads to an increase in total entropy (system plus surroundings). The direction of spontaneous change always increases the total entropy of the universe at the expense of energy available to do useful work. This is known as the second law of thermodynamics.

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