THERMOCHEMICAL CHANGES 2

QUIZ 2

what is needed in order to start the combustion of a hydrocarbon?

a match

a chemical sample consists of what?

entities ( atoms, ions, molecules ) that are in constant random motion at various speeds, rebounding elastically from collisions from each other

what is the minimum energy that colliding entities must have in order to react?

activation energy

an effective collision requires _________. collisions with the required energy have the _______.

sufficient energy,

potential to react

ineffective collision involves…

entities that rebound elastically from the collision

what are the reasons for ineffective collisions?

1) not enough energy

2) wrong orientation.

breaking bonds between atoms or ions…

require energy, making it an endothermic process ( bonded particles + energy » separated particles )

bond energy is the energy…

required to break a chemical bond.

The __________ the bond, the _____ the energy needed to..

stronger, greater, break it.

forming bonds between atoms or ions…

release energy, making it an exothermic process. ( separated particles » bonded particles + energy )

in any endothermic rxn the energy required to break bonds is…

greater than the energy released when bonds are formed.

in any exothermic rxn the energy required to break bonds is…

less than the energy released when bonds are formed

what is a catalyst

reduces the activation energy for a rxn

what does a catalyst results in?

a larger number of collisions between entities, so the rxn rate increases.

the uncatalyzed rxn proceeds…

slowly at room temp

the catalyzed rxn has a ___ ea, thus having an _____ rate ( ________ collision )

lower, increased, effective

even if catalyst is present…

the H will be the same, but the peak is LOWER

the enthalpy absorbed or produced in a given chemical rxn is…

independent of whether the rxn occurs in one step or in several steps.

if the rxn occurs in several steps..

The overall heat of rxn will be the algebraic sum of the heats of the various steps

hess’s law

the amount of energy involved in a chemical equation is the same whether the reaction occurs in one single step or in a series of smaller steps.

molar heat of formation

is the amount of enthalpy released or absorbed when one mole of a compound is formed from its elements

molar heat of decomposition

is the amount of enthalpy released or absorbed when one mole of a compound decomposes to its elements

the higher the negative molar enthalpy s compound has..

The greater that compounds stability.

lower molar enthalpy means..

stronger bonds which = to more thermal stable

how do you find △H for uncatalyzed and catalyzed reaction

△H = product EP - reaction EP

controlled variable

what stays the same

manipulated variable

what you change

responding variable

effect of manipulated variable