enthalpy & thermochemical equations (u1, ch9.1)

thermodynamics

study of energy transfer and energy changes

thermochemistry

- Study of energy changes involved in physical changes (change in state, solutions) and chemical changes (combustion, decomposition, formation, etc.)

Law of Conservation of Energy

- Energy cannot be created or destroyed but can be changed from one form to another

system

- the particles/objects under observation. (ex. solution)

- If a _______ loses energy, the surroundings gain the exact same amount of energy, and vice versa.

surroundings

- everything with which the system can exchange energy.

- everything else in the universe (outside the system)

kinetic energy

- energy of motion (energy of particles moving or thermal energy)

- more KE = higher temp

potential energy

- stored energy (energy stored in chemical bonds)

ex. ionic bonds, covalent bonds (intramolecular forces)

transfer of heat

Heat, "Q," refers to the transfer of energy between objects of different temperatures.

- Heat can be measured in Joules (J) or kilojoules (kJ)

2nd law of thermodynamics

- energy goes from hot to cold

- Every energy transfer or transformation increases the entropy of the universe.

- hot -> more energy

- cold -> less energy

ex. when you touch ice, you are not cold due to the coolness of the ice. instead, YOUR heat is lost and transferred to the ice.

Endothermic

- energy is absorbed by the system

- surroundings lose heat

- DECREASE IN TEMPERATURE

exothermic

- energy is released by the system

- temperature of surroundings gain heat

- INCREASE IN TEMPERATURE

change in energy

energy of products - energy of reactants

energy of bonds broken - energy of bonds formed

form

the amount of energy used to ______ bonds is EXOTHERMIC

break

the amount of energy used to ______ bonds is ENDOTHERMIC

greater than

when..

Energy absorbed to break bonds is ________________ energy released when bonds form

--> the reaction is ENDOTHERMIC

less than

when..

Energy absorbed to break bonds is ________________ energy released when bonds form

--> the reaction is EXOOTHERMIC

energy and enthalpy

- Enthalpy, "H," is the total internal energy of a system.

- it cannot be directly measured since it is difficult to determine the amount of stored (potential) energy within a substance

- differences in enthalpy can be calculated!

- enthalpy change, △H, communicates the difference between the enthalpy of the products and the enthalpy of the reactants

- H products = H reactants

or

- △H = Hp - Hr

one mole

molar enthalpy is the enthalpy change of ____ ______ of substance in the process

notation

△rH = enthalpy of reaction

△rH° = standard enthalpy of reaction ("°" denotes SATP conditions)

ex. CH₄O(g) + 2O₂(g) --> CO₂(g) + 2H₂O(g)

△rH = -802.5kJ (energy is released, evident due to the NEGATIVE SIGN "-", exothermic)

thermochemical equation

representing enthalpy change

- balanced chemical equation including enthalpy for reaction

ex. CH₄O(g) + 2O₂(g) --> CO₂(g) + 2H₂O(g) + 802.5kJ

H notation

- △__ __________

enthalpy is written separately from the chemical equation

ex.

CH₄O(g) + 2O₂(g) --> CO₂(g) + 2H₂O(g) + 802.5kJ

△H = -802.5kJ