thermodynamics Flashcards
what does system refer to?
the particular chemical species being studied
what does surroundings refer to?
everything that is not in a system
what does the universe consist of?
system+ surroundings
what are the different types of systems?
-open systems
-closed systems
-isolated systems
what are open systems?
-systems that can gain or lose mass and energy across their surroundings
what are closed systems?
-systems that can absorb or release energy but not mass across the boundary
what are isolated systems?
-systems that cannot exchange matter or energy with their surroundings
what are the two ways a chemical system can exchange energy with its surroundings?
-absorbing heat from or emitting heat to the surroundings
-doing work on the surroundings or having the surroundings do work on it
what is work?
-motion against an opposing force
what is heat?
-a transfer of energy due to a temperature difference
what is the formula for specific heat capacity?
-q=C Δ T
-q:heat/J
-heat capacity/J K-1
-Δ T:change in temp/K
what does heat capacity depend on?
-the size of the sample
what is an extensive property?
-a property with a value that depends on the size of the sample
what is an intensive property?
-a property with a value independent of the size of the sample
how can you convert heat capacity to an intensive property?
-by dividing by mass (you get specific heat capacity)
-by dividing by moles (you get molar heat capacity)
what is a calorimeter?
-an apparatus designed to minimise heat loss between the system and surroundings
what can ΔH be used to determine?
-whether a reaction is exothermic or endothermic
-ΔH=-ve
-ΔH=+ve
what are the standard conditions for standard enthalpy change?
-conc=1mol dm-3
-pressure=10^5 Pa (= 1 atm)
what is hess’s law?
-a method for combining known thermochemical equations in a way that allows us to calculate ΔHө for another reaction
what are the rules for manipulating thermochemical equations?
-when an equation is reversed the sign of ΔHө must also be reversed
-formula can be can be cancelled from both sides of an equation only if the substance is in an identical physical state
-if all the coefficients of an equation are multiplied or divided by the same factor, the value of ΔHө must also be multiplied or divided by the same factor
what is the standard enthalpy of combustion?
-enthalpy change at temperature T when 1 mole of a substance is completely burned in pure oxygen gas
-combustion reactions are always exothermic
what is the standard enthalpy of formation?
-the enthalpy change when 1 mole of substance is formed at 10^5 Pa & the specified temperature from its elements in their standard states
what are the factors that affects entropy?
-volume
-temperature
-physical state
-number of particles
how does volume affect entropy?
-increasing volume also increases entropy especially for gases
how does temperature affect entropy?
-the higher the temperature, the higher the entropy
-when T=0K, the atoms are in perfect order and there is minimal entropy
-when T>0K, the atoms are more disordered and there is higher entropy
-when T»0K, the atoms are further disordered and there is further increased entropy
how does physical state affect entropy?
-gases have more entropy (more ways of distributing energy) than liquids which have more entropy than solids
how does the number of particles affect entropy?
-when all other things are equal, reactions that increase the number of rot particles in the system tend to increase the entropy
what does Gibbs free energy allow us to determine?
-whether a particular chemical reaction or physical change is spontaneous
-ΔG < 0 means the reaction is spontaneous
-ΔG=0 means the reaction is at equilibrium
-ΔG>0 means the reaction is non-spontaneous
what is the equation for Gibbs free energy?
ΔG=ΔH-TΔS
