Chemistry 30 diploma prep- thermochemistry

intramolecular forces

covalent bonds and ionic bonds

intermoleculer

dipole dipole, hydrogen bond, london diperian forces

intramolecular

the glue holding a molecule together.

intermolecular

the "Velcro" between different molecules—they affect boiling point, melting point, solubility, etc.

endothermic examples

photosynthesis, boiling points, melting points

exothermic examples

combustion

endothermic

more energy is required to break bonds than is released forming new ones

exothermic

more energy is released in bond formation than is required to break bonds

enthalpy depends on

-the reaction (products and reactants)
-the coefficents of the balanced equation

when chemical reactions or phase change occurs there is an enthalpy change because

the reactants and products have different enthalpies

endothermic has a (_) sign

+

what is the source of stored potential energy

chemical bonds

enthalpy change

the energy change of a balanced equation that occurs during a chemical reaction or phase change, reflecting the difference in enthalpy between products and reactants.

Molar enthalpy

the amount of energy absorbed or released per mole of a substance during a phase change at constant pressure.

Exothermic has more energy in bond

formation, so in the reactants

endothermic has more energy in

breaking (think ender's game he broke the system) so the products

combustion (exo) reacts and

ender (endo) breaks

heating something is

endothermic because heat needs to go into the system

breaking something is

endothermic because energy must go in to break the bonds

Photosynthesis points

-fuel for the cell resp process

-eventually can be transferred into fossil fuel

-energy originated from the sun

-6 CO2 + 6 H2O →C6H12O6 + 6O2 (water vapour though)

cellular respiration points

-exothermic

-reverse of photosynthesis

combustion

hydrocarbon fuel + oxygen → carbon dioxide and water
(sooooooo basically cell resp but with choose your own fuel)

When does combustion produce water vapour

in a closed or open system

when does combustion produce liquid water?

In an isolated system like a bomb calorimeter

decomp molar enthalapy is found by?

Reversing the polarity of the formation enthalpy in the data booklet

how can you determine if products or reactants have more EP?

energy potential diagrams

what are the x and y axis for EP diagrams?

y axis is EP in KJ, x axis is progress of rxn, the diff between the products n reactants is the delta H for that equation

what are the polyatomic elements?

P4 and S8

for ranking question, if postivie KJ

that means the system is gaining that much energy to form or decompose, so it would take more energy then a neg

calorimetry assumptions

1. the transfer of energy between the system and calorimeter is 100% efficient

2. no heat escapes the calorimeter

3. the specific heat capacity of a dilute solution is the same as water 4.19j/gc

4. the density of water is 1g/mL

explain simple, flame, and bomb caloriemetry

-a reaction takes place in a polysterence cup filled with water
-a fuel is burned below a metal contaniar filled with water
-a reaction takes place inside an enclosed vessel with surrounding sleeve filled with water

Activation energy

the minimum collision energy required for a reaction

Ea and delta H details

EA has to be positive, delta H can be negative, product-reactant vs mas e - reactant e

cataylsts

alternate pathway, decreases EA, delta H stays the same

modified hess law

products - reactant , elemtents are just 0