Test 4 Flashcards
What are exothermic reactions?
Chemical reactions that release energy.
What are endothermic reactions?
Chemical reactions that absorb energy.
What are two thermochemical equations to represent exothermic reactions?
reactants —> products ΔH = -kJ
reactants —> products + kJ
What are two thermochemical equations to represent endothermic reactions?
reactants —> products ΔH = +kJ
reactants + kJ —> products
What is enthalpy?
The total of all energy (kinetic and potential) contained in a substance.
What is bond energy?
The amount of energy in one mole (kJ/mol).
What is the formula to calculate change in enthalpy?
ΔH = ∑ Hr (bonds broken) - ∑ Hp (bonds formed)
What are reaction mechanisms?
A series of reaction (more than one bump in the energy diagram).
What is Hess’s Law?
The enthalpy change of a complex reaction is equal to the sum of the enthalpy changes of the simple reactions it is composed of.
What are the two ways to calculate enthalpy change using Hess’s Law?
- Heat of formation
- Using enthalpy (kJ/mol) of each molecule
How do you calculate enthalpy change using heat of formation?
Use elementary reactions and their enthalpies to form the target reaction (like algebra). Multiply and/or reverse the sign depending on the target. Add the reactions and their enthalpies to get overall change in enthalpy (kJ).
How do you calculate enthalpy change using the enthalpy of each molecule?
Multiply and/or reverse the sign depending on the context. Add all the enthalpies to get the overall change in enthalpy (kJ).
What does an endothermic energy diagram look like?
The reactant line is lower than the product line.
What does an exothermic energy diagram look like?
The reactant line is higher than the product line.
