chapter 7

Question 1

Physical changes

Answer 1

Melting, Freezing. and boiling are examples of physical changes. A key property to a physical change is that no intramolecular bonds are made or broken, it only affects the intermolecular forces between molecules or atoms. These changes are closely related to temperature.
*pg144

Question 2

What does temperature tell us about matter?

Answer 2

Temp is a measure of the amount of internal kinetic energy (the energy of motion) that molecules have. The average kinetic energy of the molecules of a substance directly affects its state or phase. Kinetic energy is also related to the degree of disorder, or entropy. the higher the kinetic energy the greater its entropy.
*pg144

Question 3

Phase changes

Answer 3

Phase changes are simply the result of breaking (or forming) intermolecular interactions.
One of the most important: When a substance absorbs or releases heat, one of two things can happen: either its temp changes or it’s phase, but not both at the same time.
*pg144/147

Question 4

Solids, liquids, and gases

Answer 4

Solids: the most ordered and least energetic of the phases
Liquids: molecules still in contact and interact with each other, but they have enough kinetic energy to escape fixed positions. They have more internal kinetic energy and greater entropy than solids.
Gases: move freely of one another and experience very little, if any, intermolecular forces. they are the most energetic and least ordered of the phases.
*pg144/145

Question 5

phase changes that release heat and phase changes that absorb heat

Answer 5

release heat: changes that bring molecules, so condensation, freezing, and deposition
Absorb heat: changes that spread molecules out, so melting/fusion, vaporization, and sublimation.
*pg146

Question 6

heat of transition

Answer 6

The amount of energy required to complete a phase transition. symbolized: ΔH.
Heat of fusion is the amount of energy absorbed to change a solid to liquid, and heat of vaporization is the amount of energy absorbed when a liquid changes to gas
Each substance has a specific heat of transition for each phase change, and the magnitude is directly related to the strength and number of the intermolecular forces that substance experiences.
*pg146

Question 7

Heat of transition formula

Answer 7

q = n x ΔH_phase change

• • n = # of moles of the substance
• • if ΔH and q are positive, heat is absorbed, and if they’re negative heat is released.
• pg146

Question 8

Calorie and conversion bw joule and calories

Answer 8

the amount of heat required to raise the temp of 1 g of water by 1ºC. The SI unit of heat is Joule (J)
1 cal = 4.2J
*pg146

Question 9

Heat capacity

Answer 9

The amount of heat absorbed or released by a sample is proportional to its change in temp. The constant proportionality is called the substance’s heat capacity, C.

equation: q = mcΔT
- - q : heat added to (or released) by a sample
- - m = mass of the sample
- - c = specific heat of the substance
- - ΔT = temperature change
* pg147

Question 10

specific heat

Answer 10

A substance’s specific heat is an intrinsic property of that substance and tells us how resistant it is to changing its temperature.
This value also depends on the phase. It can also be given in the value of kelvin rather than celsius but since the size of a celsius degree is the same as a K, the numerical value won’t change for the substance
*pg147

Question 11

Phase transition diagram

Answer 11

aka heating curve. plots the temp of the sample vs the amount of heat absorbed. The horizontal axis represents the amount of heat added, and the vertical axis is the corresponding temperature of the substance. the flat lines are when a substance reaches its melting and boiling point. the greater the value the longer the line. heat of vaporization is always greater than heat of fusion. the sloped lines show the temp changes as heat is added.
*pg149

Question 12

Pressure and phase changes

Answer 12

At high temps, a substance can be squeezed into the liquid phase if the pressure is high enough, and at low temp a substance can enter the gas phase of the pressure is low enough.
*pg151

Question 13

Phase diagram

Answer 13

shows how its phases are determined by temp and pressure. The boundary lines bw phases represent points at which the 2 phases are in equil. Crossing a boundary line implies a phase transition. the solid phase is favoured at low temp and high pressures, while the gas phase is the opposite.
*pg151

Question 14

normal melting and boiling point in the phase diagram

Answer 14

if a horizontal line is drawn at 1 atm, the point where it crosses solid-liquid boundary is the normal mp, and where it crosses liquid-gas boundary its the normal bp.
*pg151

Question 15

Triple point in the phase diagrams

Answer 15

the temperature and pressure at which all three phases exist simultaneously in equilibrium, and therefore all phase changes are happening simultaneously.
*pg151

Question 16

Critical point in the phase diagrams

Answer 16

marks the end of the liquid-gas boundary. Beyond this point, the substance displays properties of both a liquid (such as high density) and a gas (such a low viscosity).
*pg151

Question 17

Supercritical fluid

Answer 17

A substance that is in this state of a critical point, and no amount of increased pressure can force the substance back into its liquid phase.
*pg151

Question 18

the phase diagram of water

Answer 18

water is denser in the liquid phase than in the solid phase. As a result, the solid-liquid boundary line in the phase diagram for water has slightly negative slope, as opposed to the usual positive slope for most substances. so for water an inc in pressure at constant temp can favour the liquid phase, not the solid phase like most substances.
*pg152