Enthalpy and Thermochemistry Flashcards
What is an exothermic reaction?
One that releases heat
What is an endothermic reaction?
One that requires a certain amount of heat
What is the equation for the enthalpy change (ΔH) of a reaction?
ΔH = ΔE + (PxV)
What does Hess’s law state?
ΔH[overall] = ΔH₁ + ΔH₂
What are the standard conditions for a reaction?
1 atm (pressure)
25°C
Standard physical state of element
What is the enthalpy of formation?
The enthalpy change accompanying the formation of a compound from its elements
What is bond dissociation energy?
The enthalpy change when a bond is broken
What is the equation to work out bond dissociation energy?
ΔH°[reaction] = ΣBE[reactants] - ΣBE[products]
What is the equation for calorimetry?
Q = m C ΔT
What is calorimetry?
the amount of heat required to change the temperature of a substance from T₁ to T₂
What is entropy?
the degree of disorder in a system
What does the 2nd law of thermodynamics state?
Preferred direction of a transformation comes from the transformation which requires the smallest amount of energy and creates the largest amount of disorder.
What is the equation for Gibb’s free energy (G)?
ΔG = ΔH - (T x ΔS)
When is a reaction spontaneous?
when ΔG < 0
When is a reaction in equilibrium?
when ΔG = 0
