Enthalpy Flashcards
define enthalpy change (△H)
enthalpy change is the change in heat energy content measured at constant conditions.
define standard enthalpy change of combustion
standard enthalpy change of combustion is the change in enthalpy when one mole of a substance combusts completely with excess oxygen
a reaction increases in temperature. is the reaction exothermic or endothermic and why?
this reaction is exothermic since △H is less than 0.
it is exothermic because more energy is released forming the product bonds compared to the energy absorbed in the breaking of the reactant bonds
what is a catalyst?
a catalyst increases rate of reaction of a chemical reaction by providing an alternate pathway of lower activation energy. this means that an increased amount of particles have sufficient activation energy to react, thus increasing rate of reaction.
what is the maxwell-boltzmann distribution curve?
the maxwell-boltzmann distribution curve is a curve that has number of particles on the y axis and energy of particles on x axis.
how does a catalyst affect the maxwell-boltzmann distribution curve?
it shifts the vertical line of activation more left: this means a greater area under the curve, meaning that there are an increased proportion of particles able to react, increasing rate of reaction
how does increasing temperature affect the maxwell-boltzmann distribution curve?
pulls the entire curve’s peak more right, activation energy stays the same, but because the curve is more negatively skewed, there is an increase in the amount of particles that can react due to an increase in temperature (increased kinetic energy)
what is enthalpy change’s relation to bond energy
△H = sum of bond energy of (reactants - products)
what will react faster, a reaction with high or low activation energy?
a low activation energy, as the likelihood of having more particles that have sufficient activation energy is higher
how does temperature increase rate of reaction?
- temperature of a system (increases average kinetic energy of reaction, increase proportion of particles that have sufficient energy above activation energy, increases number of collisions that can occur, increases rate of reaction)
how does concentration increase rate of reaction?
concentration increases rate of reaction as there are more reactant particles able to react. This increased proportion of reactant particles increases the number of collisions that can occur, thus increasing rate of reaction.
does pressure affect rate of reaction when reactants are not gaseous?
no, because you cannot compress solids or liquids, therefore rate of reaction would be unaffected
how do you calculate bond energy?
bond energy of reactants - bond energy of products
how do you calculate △H?
△H products - △H reactants
what must you write before doing any enthalpy calculations?
“△H products - △H reactants”
