Phases

Question 1

Physical changes

Answer 1

ex ) melting, freezing and boiling
no intramolecular bonds are made or broken
in physical changes only the intermolecular forces between the molecules or atoms are affected . ( disruption of attractive interactions between the molecules)
- intramolecular bonds are not affected ! : ex ) molecules of H20 are not changed into something else

Question 2

physical changes are closely related to temperature

Answer 2

temp is the measure of amount of the internal kinetic energy that molecules have.
the average kinetic energy of the molecules of a substance directly affect its state or phase weather its a solid, liquid or gas.

Question 3

kinetic energy is also related to the degree of disorder or

Answer 3

entropy! higher the kinetic energy of the molecules the greater its entropy

Question 4

what causes the phase transitions as the temp increases?

Answer 4

phase changes are result of breaking or forming of intermolecular interactions.

Question 5

what is condensation?

Answer 5

gas to a liquid

Question 6

what is vaporization?

Answer 6

liquid to a gas

Question 7

what is sublimation ?

Answer 7

solid to a gas

Question 8

what is deposition?

Answer 8

gas to a solid

Question 9

phase changes that bring molecules together such as deposition , condensation, freezing do what?

Answer 9

release heat

Question 10

phase changes that spread out molecules

Answer 10

absorb heat

Question 11

heat of transition (delta H)

Answer 11

is the amount of energy needed to complete a transition
ex) heat of fusion : solid to a liquid
heat of vaporization : liquid to gas

Question 12

each substance has a specific heat of transition for each phase change and the magnitude is related to the ?

Answer 12

strength and the number of the intermolecular forces that the substance experiences

Question 13

q=ndelaHphase change

Answer 13

delta H : heat of transition 
q= amount of heat 
n= number of moles of a substance 
if h and q are pos : heat is abs 
and if h and q are negative : heat is released

Question 14

what is a calorie?

Answer 14

amount of heat needed to raise the temp of 1 g of water by 1 degrees Celsius.
the SI unit of heat and of all forms of energy is a joule !
1 cal = 4.2 joules
what we popularly call a calorie is actually a kilocalorie 10^3 calorie! and is written with a capital C

Question 15

when a substance is undergoing a phase change it absorbs or releases heat without ?

Answer 15

a change in the temp

Question 16

in between phase changes, matter can absorb or release energy without undergoing transition. we observe this as

Answer 16

an inc or dec in temp

Question 17

the amount of heat absorbed or released by a sample is proportional to its change in temperature .

Answer 17

this constant of proportionality is called the substance's heat capacity C which is the product of its specific heat c and its mass m . 
q= mc delta T 
q= heat added or released by a sample 
m= mass 
c= specific heat of the substance 
delta T:  temp change.

Question 18

what is the substances specific heat?

Answer 18

intrinsic property - tells us how resistant it is to changing its temp.
so a higher specific heat means its more resistant to changing its temp.
a higher specific heat means it will undergo a smaller change in temperature

Question 19

the specific heat of a substance also depends on ?

Answer 19

phase!

ex) specific heat of ice is diff than that of liquid water

Question 20

molecules that have strong intermolecular forces will tend to have a ___ specific heat

Answer 20

high

Question 21

a substance heat of vaporization is always ___ then the heat of fusion

Answer 21

higher

Question 22

when a phase change is not occurring you use

Answer 22

q=mcat

bc there will be a CHANGE IN TEMP

Question 23

when a phase change is occurring you use.

Answer 23

q=mh

h could be heat of fusion or the heat of vaporization

Question 24

the phase of a substance dosent just depend on the temperature it also depends on?

Answer 24

pressure!

Question 25

what is the triple point?

Answer 25

temp and pressure at which all three phases exist simultaneously in equilibrium. so all phase changes are happening simultaneously.

Question 26

what is the critical point?

Answer 26

marks the end of the liquid -gas boundary!
beyond this point, its called a supercritical fluid : it has properties of both liquid and gas , and the liquid and gas phases are not distinct!
no amount of increases pressure can force the substance back to its liquid phase.

Question 27

why is water different?

Answer 27

water is denser in the liquid phase then in the solid phase . that’s why the solid-liquid boundary line in the phase diagram for water has a negative slope .

Question 28

water

Answer 28

if you increase the pressure at constant temp, liquid phase is favoured more then the solid. ex) skating on ice, pressure will inc as you skate, and the ice will turn into liquid
vs CO2 , solid co2 would never turn liquid with increase in pressure.