THERMOCHEMICAL CHANGES UNIT ( 1&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

enthalpy change

basis of all change is due to energy transformations, sum of all eK + eP

what takes solar energy from the sun and transforms it to _______ of glucose which in turn is transformed by…

photosynthesis

chemical energy

living things to thermal energy and mechanical energy of movement

what is a stored form of chemical energy in which its origin can be traced back to the solar energy of the sun?

fossil fuels

is cell resp exo or endo?

exo

is photosyn exo or endo?

endo

what occurs in the body, cell resp or photosyn

cell resp

what occurs in plants, cell resp or photosyn

photosyn

examples of exothermic changes

combustion, hot packs, cell resp

examples of endothermic changes

cold pack, photosyn, evaporation, perspiration

What is the Law of conservation of energy

energy cannot be created or destroyed

energy can be changed or converted from one form or another

What is the Law of heat exchange or transfer?

heat energy flows ( moves ) from a hot to a cold object until thermal equilibrium is reached ( both are at the same final temperature )

total heat lost equals..

total heat gained

what is thermochemistry

the study of energy changes during a chem reaction

what requires to be working in an isolated system

thermochemistry

whats an isolated system

no matter or energy exchange

energy gained by the chemical system is equal to what

the energy lost by the calorimeter and its contents, as long as both the calorimeter and its contents ( surroundings ) are part of an isolated system

what is the main assumption when using a calorimeter

no heat is transferred to the outside of the calorimeter

kinetic molecular theory

smallest particles of any substance are in continuous motion

what is released when collisions occur

energy

energy of motion is given what name

kinetic energy

what happens if there is enough energy produced upon collision?

reaction or change will take place

temperature of a substance is a measure of the average…

kinetic energy of the particles of the substance

substances at the same temp are believed to have particles with..

the same average kinetic energy

if what of the reactants and products are the same what does it indicate?

temp

no change in eK of the system

if temperature is kept constant, then the only change of enthalpy is the result of a change in…

eP

what is enthalpy change

difference between the enthalpy of the products and the enthalpy of reactants.

exothermic reaction is represented by a ____ enthalpy change

negative

endothermic reaction is represented by a ____ enthalpy change

positive

whats molar enthalpy of reaction

enthalpy change when one mole of a specified chemical undergoing a change in the system at constant pressure

what are the four methods of communicating enthalpies

molar enthalpy

enthalpy changes for 4 moles of the substance

balance thermochemical equation for 4 moles

ep diagram for 4 moles

what does ep diagram represent

it shows change in ep during a chem reaction

Cell resp equation

C6H12O6+6O2→6CO2+6H2O+2802.7KJ

Photosyn equation

6CO2+6H2O+2802.7KJ→C6H12O6+6O2