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final exam Flashcards

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1
Q

why do most chemical reactions involve heat?

A

because breaking bonds required energy and forming bonds releases energy, (and heat is energy)

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2
Q

what is and endothermic reaction? an exothermic reaction

A

endothermic reaction- a reaction in which energy is overall required or absorbed
exothermic reaction- a reaction in which energy is overall released

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3
Q

what is entropy?

A

disorder

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4
Q

what is a spontaneous reaction?

A

a reaction that occurs without any continuous outside intervention

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5
Q

2AB2 (g)—>A2 (g) + 2B2 (g)

ΔH is either positive or negative 117 kj/mol for this reaction. which is the correct value. explain?

A

+117 kj/mol; because it is a decomposition reaction and those are endothermic

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6
Q

2AB2 (g)—>A2 (g) + 2B2 (g)

rewrite the equation as a thermochemical equation with either a positive or negative ΔH

A

2AB2 (g) + 117 kj/mol—>A2 (g) + 2B2 (g)

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7
Q

2AB2 (g)—>A2 (g) + 2B2 (g)

ΔS is either positive or negative .080 kj/mol K for this reaction. which is the correct value? explain?

A

+.080 kj/mol; because there is more disorder on the product side that the reactant side, so more minus less would equal a positive entropy

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8
Q

some reactions are always spontaneous and some reactions are never spontaneous. however, some reactions that are no spontaneous can be made spontaneous. how?

A

some reactions that are no spontaneous can be made spontaneous when in an environment with a different temperature that can make it spontaneous (such as how ice will not melt in a cold environment, but it will melt in a warm/room temperature environment)

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9
Q

gases have a very low density. what assumption in the kinetic molecular theory of gases explains why?

A

gases particles are separated by large distances, so they have a low density

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10
Q

gases are fluids. what does this mean? explain why gases have this property in terms of the kinetic molecular theory?

A

gases being fluids means that they flow; the particles of a gas are in constant random motion and they don’t have strong attractive forces

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11
Q

what is pressure caused by

A

collisions of particles

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12
Q

what happens to atmospheric pressure as altitude increases?

A

as altitude increases, atmospheric pressure decreases

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13
Q

why are gases not ideal? (give two reasons)

A

because their particles take up space and they exhibit slight attractive forces

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14
Q

under what conditions of temperature and pressure do real gases most closely have have as ideal gases?

A

to make a gas closer to an ideal gas, the temperature must be high and the pressure must be low

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15
Q

gay-lussac’s law examines the relationship between pressure and temperature at constant volume. what happens to the pressure of a gas if the temperature increases? explain

A

when temperature increases, pressure increases because the gas particles will have more energy and hit the sides of the container more often

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16
Q

if the temperature is constant and the volume of a gas decreases, what happens to the pressure? explain

A

if the volume of a gas decreases, the pressure increases because the gas particles will have less room to move in and will hit the container more often

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17
Q

hot air balloons rise. a balloon filled with helium also rises. explain each

A

a hot air balloon rises because it is full with gas and as the temperature increases, the volume increases; a balloon with helium rises because helium is a gas with a smaller molar mass. do a gas to lift an object, it has to have a small density, which can be achieved by heating the gas and selecting one with a smaller molar mass

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18
Q

you are given 1 mole of helium gas and an identical container of 1 mole of oxygen gas. both gases are at STP. determine whether each of the following statements are true or false

a. both are ideal gases
b. both gas samples have the same kinetic energy
c. both gases have the same mass
d. both gas particles have the same number of particles
e. both gas samples have the same density

A

a. false
b. true
c. false
d. true
e. false

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19
Q

list the types of intermolecular forces from strongest to weakest

A

hydrogen bonds
dipole-dipole forces
london dispersion forces

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20
Q

what is the key difference between a dipole-dipole force and a dispersion force?

A

dipole-dipole forces result from permanent dipoles, whereas dispersion forces result from temporary dipoles

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21
Q

why do liquids, but not solids, take the shape of their containers?

A

solids have such strong intermolecular forces that make the particles tightly packed, so they have a definitive shape and volume

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22
Q

of the three states of matter, explain which have a definite volume, explain why each state has or does not have a definite volume

A

liquid and solid have definite volume. liquids have a definite volume because their intermolecular forces are so strong that particles cannot separate; solids have a definite volume because their intermolecular forces are strong and make their particles tightly packed; gases do not have a definite volume because their particles have weak intermolecular forces (and loosely packed particles)

23
Q

what is the difference between a crystalline and an amorphous solid? what is true of the melting point of each type of solid?

A

crystalline solids have particles with highly organized, repeating patterns, but amorphous solids have particles with no repeating patterns and are randomly organized; along with that, amorphous solids soften before they melt and have a (wide) range of temperatures where they experience melting, but crystalline solids have a definite melting point (and do no soften)

24
Q

what happens to a substance’s kinetic energy as it boils? its potential energy?

A

a substance’s KE remains constant as it boils (because temp is constant), and its PE increases (because liquid is turning to gas, which gives the particles more freedom to move)

25
Q

one property of a liquid is viscosity. what is viscosity? how does a substance’s viscosity relate to it’s intermolecular forces?

A

viscosity- the friction or resistance to motion of a liquid’s particles that can move past each other
the stronger the intermolecular forces, the more/greater the viscosity

26
Q

what happens to the surface tension of a liquid if it’s temperature increases? explain

A

if temperature increases, surface tension decreases because intermolecular forces are being weakened/broken

27
Q

a system that consist of a solid and a liquid is are equilibrium

what is equilibrium?

A

the dynamic condition in which two opposing changes in a system occur at equal rates; in this case, freezing and melting are in equilibrium

28
Q

how does the number of solid particles compare to the number of liquid particles?

A

there does not have to be an equal number of solid and liquid particles or a certain ration of the amounts of these states for the system to be in equilibrium; the two numbers can vary

29
Q

if the temperature increases, what happens to the system?

A

if the temperature increases, melting would increase and the system would not be in equilibrium

30
Q

according to le chatelier’s principle, what will happen to the system next? be specific

A

when something makes the system to not be in equilibrium, the system will adjust to return to equilibrium; in this case, the rate of freezing would increase to be equal to the rate of melting and be in equilibrium

31
Q

list the six state changes, distinguishing between endothermic and exothermic changes

A

endothermic: melting, vaporization, sublimation
exothermic: freezing, condensation, deposition

32
Q

why is the molar heat of vaporization for a substance always greater than its molar heat of fusion? be specific

A

it required more energy to break intermolecular forces than to weaken them, and vaporization involves breaking them, whereas melting involves just weakening them

33
Q

what is the triple point on a phase diagram?

A

the point in which all three states of matter are in equilibrium

34
Q

what is the critical point of a substance in a phase diagram?

A

the temperature above which the substance is always a gas

35
Q

what is a solution? identify and define two components of a solution

A

solution- a homogenous mixture of two or more substances in a single physical state

two components or a solution are solvent and solute; solvent is the substance that dissolved another substance and has no state change or it is present in the greatest amount, but solute is the substance that gets dissolved and it’s physical state changes or it is present in the least amount

36
Q

vinegar dissolved in water. oil does not dissolve in vinegar but it does dissolve in toluene. classify each substance (vinegar, water, oil, and toluene) as polar or nonpolar

A

vinegar- polar
water- polar
oil- nonpolar
toluene- nonpolar

37
Q

what is the effect of temperature on the solubility of a gaseous solute in a liquid solvent?

A

as temperature increases, solubility increases

38
Q

what is a colligative property? list three example of colligative properties

A

a colligative property is a property that is determined by the presence and concentration of a solute and how various aspects of the solution will be changed because of this

vapor pressure, freezing point, boiling point

39
Q

20 mL of apple juice is diluted with 10mL of water. which substance is the solute?

A

water

40
Q

why does stirring increase the dissolving rate?

A

because it allows fresh particles of solvent to contact solute particles quicker

41
Q

describe the particles of a solution. list at least two different points

A

particles of a solution all look the same, are spread out evenly, and do not settle (meaning the solution does not have to be shaken)

42
Q

a gas mixture is made of 25 g oxygen, 35 g nitrogen, and 45 g helium

a. is this a solution?
b. if this is a solution, what is the solvent?

A

a. yes

b. helium

43
Q

list three properties of acids and three properties of bases

A

acids: taste sour, react with metals to produce H2, good conductors or electricity
bases: taste bitter, feel slippery, corrosive (very reactive)

44
Q

which would you expect to be a better conductor: a weak acid or a strong base?

A

strong base

45
Q

what is the difference between a strong and a weak acid? give one example of each

A

strong acids completely dissociate, but weak acids do not completely dissociate (separate into ions); a strong acid is sulfuric acid and a weak acid is citric acid

46
Q

why are Ka values not given for strong acids?

A

strong acids completely dissociate, so when plugging in 0 in the expression to solve for Ka, it results as i define because 0 cannot go into any number

47
Q

why is the arrhenius definition of an acid not sufficient? what does the bronsted-lowry definition of an acid state?

A

the arrhenius definition of an acid is not sufficient because it required water, but not all acids (and bases) go into/work with water; the bronsted-lowry definition of an acid statesban acid is a proton (H+) donor

48
Q

in a titration, how do you know when to stop adding base?

A

when the indicator (such as phethphalen) mixed with acid turns to a different color and status that color after adding a certain amount of base

49
Q

what is oxidation? what is reduction?

A

oxidation- a process in which electrons are lost

reduction- a process in which electrons are gained

50
Q

why must a reduction reaction and an oxidation reaction always occur simultaneously?

A

because electrons cannot randomly be lost or gained in a reaction, a reducing agent and oxidizing agent must give or take electrons (depending on which agent they are)

51
Q

what two thing must always be balanced in a redox reaction?

A

charge and atoms

52
Q

what is electrochemistry?

A

electricity related to applications of redox reactions

53
Q

do gases have mass? how could you prove your answer using common materials found in a lab

A

yes; you could weigh an empty balloon and find it’s mass, and then weigh the balloon when it is filled with air and find it’s mass

chemistry (16 decks)

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