thermodynamics

Question 1

what does system refer to?

Answer 1

the particular chemical species being studied

Question 2

what does surroundings refer to?

Answer 2

everything that is not in a system

Question 3

what does the universe consist of?

Answer 3

system+ surroundings

Question 4

what are the different types of systems?

Answer 4

-open systems
-closed systems
-isolated systems

Question 5

what are open systems?

Answer 5

-systems that can gain or lose mass and energy across their surroundings

Question 6

what are closed systems?

Answer 6

-systems that can absorb or release energy but not mass across the boundary

Question 7

what are isolated systems?

Answer 7

-systems that cannot exchange matter or energy with their surroundings

Question 8

what are the two ways a chemical system can exchange energy with its surroundings?

Answer 8

-absorbing heat from or emitting heat to the surroundings
-doing work on the surroundings or having the surroundings do work on it

Question 9

what is work?

Answer 9

-motion against an opposing force

Question 10

what is heat?

Answer 10

-a transfer of energy due to a temperature difference

Question 11

what is the formula for specific heat capacity?

Answer 11

-q=C Δ T
-q:heat/J
-heat capacity/J K-1
-Δ T:change in temp/K

Question 12

what does heat capacity depend on?

Answer 12

-the size of the sample

Question 13

what is an extensive property?

Answer 13

-a property with a value that depends on the size of the sample

Question 15

what is an intensive property?

Answer 15

-a property with a value independent of the size of the sample

Question 16

how can you convert heat capacity to an intensive property?

Answer 16

-by dividing by mass (you get specific heat capacity)
-by dividing by moles (you get molar heat capacity)

Question 17

what is a calorimeter?

Answer 17

-an apparatus designed to minimise heat loss between the system and surroundings

Question 18

what can ΔH be used to determine?

Answer 18

-whether a reaction is exothermic or endothermic
-ΔH=-ve
-ΔH=+ve

Question 19

what are the standard conditions for standard enthalpy change?

Answer 19

-conc=1mol dm-3
-pressure=10^5 Pa (= 1 atm)

Question 20

what is hess’s law?

Answer 20

-a method for combining known thermochemical equations in a way that allows us to calculate ΔHө for another reaction

Question 21

what are the rules for manipulating thermochemical equations?

Answer 21

-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

Question 22

what is the standard enthalpy of combustion?

Answer 22

-enthalpy change at temperature T when 1 mole of a substance is completely burned in pure oxygen gas
-combustion reactions are always exothermic

Question 23

what is the standard enthalpy of formation?

Answer 23

-the enthalpy change when 1 mole of substance is formed at 10^5 Pa & the specified temperature from its elements in their standard states

Question 24

what are the factors that affects entropy?

Answer 24

-volume
-temperature
-physical state
-number of particles

Question 25

how does volume affect entropy?

Answer 25

-increasing volume also increases entropy especially for gases

Question 26

how does temperature affect entropy?

Answer 26

-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

Question 27

how does physical state affect entropy?

Answer 27

-gases have more entropy (more ways of distributing energy) than liquids which have more entropy than solids

Question 28

how does the number of particles affect entropy?

Answer 28

-when all other things are equal, reactions that increase the number of rot particles in the system tend to increase the entropy

Question 29

what does Gibbs free energy allow us to determine?

Answer 29

-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

Question 30

what is the equation for Gibbs free energy?

Answer 30

ΔG=ΔH-TΔS