Princeton Ch 7 - Phases

Question 1

A key property of physical change is that no ___ bonds are made or broken; a physical change affects only ___forces between molecules.

Answer 1

A key property of physical change is that no INTRAmolecular bonds are made or broken; a physical change affects only INTERmolecular forces between molecules or atoms. When ice melts, the molecules of H2O doesn’t change.

Question 2

Temperature.

Answer 2

Temperature is a measure of the amount of internal kinetic energy (the energy of motion) that molecules have.

Question 3

In general, the ___ the average kinetic energy, the greater the entropy.

Answer 3

HIGHER.

Question 4

What are phase changes?

Answer 4

Phase changes are simply the result of breaking (or forming) INTERMOLECULAR (LDF, dipoles, H bonding, etc.) interactions.

Question 5

Solids are (most/least) ordered and (most/least) energetic of the phases.

Answer 5

Solids are most ordered and least energetic of the phases. As solids absorb heat, their temp increases, meaning the average KE of the molecule increases. This causes molecules to move around more, loosening the IM forces.

Question 6

True or false. Molecules in the gas phase move freely of one another and experience very little, if any, IM forces.

Answer 6

True. Gases are the most energetic and least ordered of the phases.

Question 7

Another word for melting, going from solid to liquid.

Answer 7

FUSION.

Question 8

Going from gas to solid.

Answer 8

Deposition.

Question 9

Going from solid to gas.

Answer 9

Sublimation.

Question 10

Going from gas to liquid.

Answer 10

Condensation.

Question 11

The amount of energy required to complete a transition is called:

Answer 11

The heat of transition.

Question 12

True or false. When a substance absorbs enough heat, its temperature, and phase changes.

Answer 12

FALSE. When a substance absorbs or releases heat, one of two things can happen: either its temperature changes OR it will undergo a phase change but not both at the same time.

Question 13

How can you find the amount of heat (q) absorbed or released?

Answer 13

q = n x ΔHphase change; ΔH = E required to complete a transition
q = mcΔT; m = mass, c = specific heat of substance; T = temperature change

Question 14

Specific heat.

Answer 14

An intrinsic property of a substance that tells us how resistant it is to changing its temperature. Water has a really high specific heat (1c/g).

Question 15

Does the specific heat also depend upon phase? In other words, is the c of water the same when it’s liquid and gas?

Answer 15

NO. The specific heat of a substance also depends on the phase. The specific heat of ice is different from that of liquid water.

Question 16

Specific heat may be given in terms of Kelvins rather than Celcius. Should you be careful with units in this case?

Answer 16

YES - you should always be wary of units. But, if the two temperatures differ by 1C, they also differ by 1K; hence the numerical value of the specific heat won’t be any different if Kelvins are used . 0C = 273.15K; 10C = 283.15K

Question 17

Since m and q are constants in q = mcΔT, ΔT is ___(inversely/directly) proportional to c. So, the substance with the greatest specific heat will undergo the smallest change in temperature.

Answer 17

Since m and q are constants in q = mcΔT, ΔT is INVERSELY proportional to c. So, the substance with the greatest specific heat will undergo the smallest change in temperature

Question 18

True or false. As you increase the temperature of a substance to melt it, that substance will continue to rise in temperature until the gas

Answer 18

As heat is added to a solid, its temperature increases until it reaches its melting point. At this point, absorbed is used to use change the phase to liquid, not to increase the temp. Once the sample has been completely melted, additional heat again causes its temperature to rise, until the boiling point is reached. At this point, absorbed heat is used to change the phase to gas, not to increase temp.

Question 19

True or false. During a phase transition, the temperature of the substance doesn’t change.

Answer 19

TRUE.

Question 20

Given that a solution containing ice and water is at equilibirum with its environment, the temperature must be __ at 1atm.

Answer 20

O degrees Celcius.

Question 21

What do boundary lines in phase diagram represent?

Answer 21

The boundary lines between phases represents points at which 2 phases are in eq. Ex. a glass of water at 0C containing ice cubes is a 2 phase system, and if its temp and pressure were ploted in a phase diagram, it would be on the solid-liquid boundary line.

Question 22

Crossing a boundary line on a phase diagram implies ____

Answer 22

Crossing a boundary line on a phase diagram implies a PHASE TRANSITION

Question 23

The solid phase is favored at __ temperatures and ___ pressures while the gas phase is favored at___ temps and ___ pressures

Answer 23

The solid phase is favored at low temperatures and high pressues while the gas phase is favored at high temps and low pressures

Question 24

If we draw a horizontal line at the 1atm pressure level, the point that crosses the solid liquid boundary is the normal ___, and the temp at the point where the line crosses the liquid-gas boundary is the NORMAL ____.

Answer 24

If we draw a horizontal line at the 1atm pressure level, the point that crosses the solid liquid boundary is the normal MELTING POINT, and the temp at the point where the line crosses the liquid-gas boundary is the NORMAL BOILING POINT.

Question 25

What is the triple point on a phase diagram.

Answer 25

The triple point is the temp and pressure at which all three phases exist simultaneously in equilibrium, and therefore all phase changes are happening simultaneously.

Question 26

What is the critical point of a phase diagram. Superficial fluid?

Answer 26

The CP marks the end of the liquid gas boudnary. Beyond this point, the substance displays properties of both a liquid (like high density) and a gas (like low viscosity). If a substance is in this state, where liquid and gas phase aren’t distinct, it’s called a supercritical fluid, and no amount of increased pressure can force the substance back to the liquid phase.

Question 27

What makes water’s phase diagram unique?

Answer 27

Water is the most common of a handful of substances that are denser in the liquid phase than solid. The solid-liquid boundary has a slightly NEGATIVE slope, as opposed to the usual positive slope. For H2O, an increase in pressure at a constant T can favor the LIQUID phase, not the solid like most other substances. Ex. Ice skater’s blade weight increases pressure, melting the ice underneath.