C5 energy Flashcards
what is the minimum energy needed to start a reaction?
the activation energy
for a reaction to occur the the bonds in the reactant must
be broken
chemical bonds and atoms contain stored of energy we call
enthalpy
if the products have less enthalpy the reactants there has been a
negative enthalpy change
in a negative enthalpy change the energy had gone from the reaction to
the surroundings
if the products have more enthalpy than the reactants there has been a
positive enthalpy change
in a positive enthalpy change the energy has been taken from the surroundings and moves into
the reaction
in a chemical reaction we cannot measure the enthalpy of the reactants or products but can
measure the temperature of the surroundings
if a reaction is exothermic the 🔺H sign is
negative
if a reaction is endothermic the 🔺H sign is
positive
exothermic means
energy is released from the reaction and into the surroundings resulting in temperature increase
endothermic means
energy is taken in to the reaction from the surroundings and the temperature decreases as the surroundings loses energy
examples of exothermic reactions are
displacement, precipitation or combustion reactions
how can you investigate the energy change in a chemical reaction?
use a thermometer to measure the initial and final temperature before and after a reaction. use a constant volume; concentration, mass of reactants. use a polystyrene cup and lid to insulate the reaction and prevent heat loss to the surroundings.
what is a displacement reaction?
more reactive element replacing a less reactive one
