Energy Flashcards
What is energy
Energy is the ability to do work or transfer heat
Kinetic energy
energy of motion
Potential energy
the energy a motionless body has due to its position and its composition.
Exothermic
when energy leaves the system and goes out into surroundings. temperature decrease in system
How long does transfer of heat as energy continue?
until thermal equilibrium is achieved. i.e. both objects are at the same temperature.
System vs surrounding
System is being studied. Surroundings are everything around the system.
Endothermic
When energy enters the system from the surroundings. temperature of system increases.
Internal energy in a chemical system
the sum of the potential and kinetic energies inside the system. i.e. sum of energies of atoms, molecules, ions and the bonds between them. we usually measure change in internal energy. U
Q
heat absorbed or lost
heat enters system?
delta U >0 and q= +
heat leaves system?
delta U < 0 and q= -
does temperature change during a phase change?
no
isothermal process
a process where there is a change of a system but the temperature remains constant eg. phase changes
examples of endothermic phase changes
when you sweat, there’s water on your skin and heat is required for that water to evaporate. So heat is taken from your body and used to evaporate it.
Example of exothermic phase change
when muggy water condenses onto your skin, it releases energy. vapour——>water
Enthalpy
heat transferred between system and surroundings under conditions of constant pressure.
Change in enthalpy
change in internal energy at constant volume
endothermic phase changes
sublimation, melting/fusion, vaporisation
exothermic phase changes
deposition, condensation, freezing
First Law of Thermodynamics
The total internal energy of an isolated system is constant.
state function
no matter which path is taken, the results are the same. eg. enthalpy
what apparatus measures heat of combustion?
bomb calorimeter
Hess’s Law
the overall enthalpy change of the reaction is equal to the sum of all the enthalpy changes of individual steps of the reaction.
What is enthalpy of formation
the enthalpy change of a reaction when 1 mole of a compound is formed from its elements. always reported at standard conditions i.e. 1 atm and 25 degrees celcius
