5,6,7 Enthalpy, Kinetics, Equilibrium Flashcards
enthalpy
chemical energy inside a substance
bond enthalpy
the energy needed to break one mole of bonds in a gaseous molecule
what is the enthalpy change for an exothermic reaction?
release energy to surrounding → product have less enthalpy (energy) than reactant → ∆H negative
what happens to the temperature of surrounding during an endothermic reaction?
absorb heat energy from surrounding → temperature of surrounding decrease
standard conditions means
- pressure = 100kpa
- concentration = 1mol/dm^3
- Each substance involved in the reaction is in its standard state (solid, gas or liquid)
standard enthalpy change of reaction
the enthalpy change when molar quantities of reactants react to form products under standard conditions
standard enthalpy change of formation
the enthalpy change when 1 mole of compound is formed from its elements under standard conditions
standard enthalpy change of combustion
the enthalpy change when 1 mole of a substance is completely burnt in excess oxygen under standard conditions
standard enthalpy change of neutralization
the enthalpy change when 1 mole of water is formed reacting an acid and base under standard conditions
exothermic！！
specific heat capacity
the energy needed to raise the temperature of 1kg of a substance by 1K
observations for exothermic reactions
- surrounding gets warm
- pop sound
activation energy (Ea)
minimum energy needed for molecules to have successful collisions (reaction)
catalyst
increases reaction rate by providing an alternative pathway of lower Ea; without being chemically changed by the reaction
rate of reaction
change in the concentration of a reactant or product / unit time
Explain, using the Maxwell–Boltzmann distribution, why increasing the temperature increases the rate of a chemical reaction
- higher temperature = higher average kinetic energy of molecules → more molecules have Ek > Ea → more successful collisions per unit time → higher rate of reaction
- higher average kinetic energy of molecules → molecules move faster → more frequent collisions → more successful collisions per unit time
A state of dynamic equilibrium is reached in a closed system when
the rates of forward and backward reactions are equal
equilibrium constant, Kc =
[product] / [reactant]
[C]^c [D]^d / [A]^a [B]^b
where [ ] is concentration, raised to the power of the coefficients (moles)
Does a catalyst have effect on the position of equilibrium or Kc?
NO! Catalysts only helps the reaction to reach equilibrium faster.
Kc is only affected by
temperature
What happens to Kc if you double the moles of all reactants and products?
Kc^2
What happens to Kc if you reverse the reactants and products?
1/Kc
reaction quotient, Q
the ratio of products and reactants for a reaction that has NOT yet reached equilibrium; calculated in the same way as Kc
Le Chatelier’s principle
if a change is made to a system at dynamic equilibrium, the equilibrium position moves to oppose the change
Explain what happens to the equilibrium position when the concentration of reactant (LHS) increases
equilibrium moves to the product side (RHS) and favors forward reaction
Explain what happens to the equilibrium position when the pressure increases
equilibrium moves to the side with less molecules (number of moles) to decrease the pressure again
*this is only for gas molecules!
Explain what happens to the equilibrium position when the temperature increases
equilibrium moves to the endothermic direction to reverse the change
