Energetics Flashcards
What is an exothermic reaction?
A reaction that gives out energy to the surroundings. The products end up with less energy than the reactants. The Enthalpy change will be negative.
What is Enthalpy Change?
The heat energy transferred in a reaction at constant pressure.
The reactants and products were in the standard states.
What is an endothermic reaction?
A reaction that takes in energy from its surroundings. The products end up with more energy than the reactants. The enthalpy change is positive.
What are bond enthalpies?
The energy needed to break or form a bond between two atoms.
What type of reaction is bond breaking?
Energy is required to break bonds so it is endothermic.
What type of reaction is bond formation?
Energy is released when bonds are so formed so this is exothermic.
Why use mean bond enthalpies?
Energy required to break an individual bond can change depending on where it is.
Calculate the overall enthalpy change of reaction:
Enthalpy change of reaction = total energy absorbed - total energy released
Standard enthalpy change of reaction
The enthalpy change when reaction occurs in the molar quantities shown in the chemical equation, under standard conditions and with reactants and products in standard states.
Standard enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions.
Standard enthalpy change of combustion
The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states.
What is Hess’s Law?
The total enthalpy change of a reaction is always the same, no matter which route is taken.
