Gas Laws
0.250‑L sealed cylinder at STP contains an ideal gas. If the temperature is held constant and the volume is reduced to 0.125 L0.125 L, what happens to the pressure? Explain using the appropriate gas law and show proportional reasoning.
Pressure doubles (Boyle's law, P1V1=P2V2P1V1=P2V2).
Define specific heat capacity and write the formula used to calculate the heat absorbed when a mass mm of a substance changes temperature by ΔTΔT.
q=mcΔT.
On a heating curve that goes from solid to gas, which segment corresponds to boiling: Identify and explain.
Boiling = horizontal segment at boiling point.
Which physical quantity represents the average kinetic energy of particles in a sample of matter?
Temperature.
Classify bronze (an alloy of copper and tin with variable composition) as element, compound, mixture, or substance and justify in one sentence.
Bronze = mixture (alloy) because composition varies.
A gas sample has a volume of 2.0 L at a pressure of 100 kPa. If the pressure is increased to 250 kPa at constant temperature, what is the new volume?
V₂ = 0.80 L
How many joules are required to raise the temperature of 100.0 g100.0 g of water from 20.0∘C20.0∘C to 50.0∘C50.0∘C? Use specific heat of water c=4.18 J/g⋅Kc=4.18 J/g⋅K and show your calculation.
q=(100.0)(4.18)(50−20)=(100)(4.18)(30)=12540 J.
In the provided uniform heating graph with labeled segments A–E, which segments correspond to times when added heat increases potential energy while kinetic energy remains constant? Explain why.
Segments B and D (flat segments at melting and boiling) represent added heat increasing potential energy while kinetic energy (temperature) remains constant.
List one physical property and one chemical property of carbon disulfide (CS₂) based on the provided passage (CS₂ is a colorless liquid with an offensive odor; vapors are flammable).
Physical: colorless liquid, odor (physical observation); Chemical: vapors flammable (flammability).
Given particle diagrams showing monatomic particles and two‑atom bonded molecules, describe how you would identify which diagram represents a mixture of an element and a compound (features to look for).
Look for single‑atom symbols (element) plus multi‑atom bonded groups of a different type (compound) in same diagram.
A gas in a sealed container has a pressure of 101 kPa at 300 K. What will the pressure be if the temperature increases to 450 K?
P₂ = 152 kPa
A 5.00‑gram sample of liquid ammonia at 210 K is heated to 240 K (no phase change). Using c=4.71 J/g⋅Kc=4.71 J/g⋅K for liquid NH₃, calculate the heat absorbed during this interval (time AB on the partial heating curve).
q=mcΔT=5.00×4.71×(240−210)=5.00×4.71×30=706.5 J.
Describe in words the particle behavior during the segment where melting occurs versus the segment where temperature rises in the liquid phase. Emphasize energy changes and particle spacing.
Melting: particles gain separation (potential energy rises) but vibrational motion still present; liquid warming: particles move faster (kinetic energy rises), spacing roughly constant.
Explain why boiling is represented by a flat (horizontal) segment on a heating curve. Describe what happens to kinetic and potential energy during that segment.
During boiling, added heat converts liquid to gas (potential energy increases) while temperature (kinetic energy) remains constant.
Which of the following substances can be decomposed by chemical means: ammonia, oxygen, phosphorus, silicon? Explain your reasoning briefly.
Ammonia (can be decomposed chemically into elements/other compounds) ammonia (a compound) vs oxygen, phosphorus, silicon (element).
A gas occupies 2.5 L at 300 K. What will be the volume of the gas at 450 K if pressure remains constant?
V₂ = 3.75 L
Calculate the minimum amount of heat required to completely melt 20.0 g20.0 g of ice at its melting point if the heat of fusion of water is 334 J/g334 J/g. Show the formula and numeric answer.
q=mΔHf=20.0×334=6680 J.
A partial heating curve for ammonia shows AB rising from 210 K to 240 K, then BC flat at 240 K. For a 5.00‑g sample, calculate the total heat absorbed during AB and BC using the given constants: cℓ=4.71 J/g⋅K, heat of fusion =332 J/g, heat of vaporization =1370 J/g. (Provide numeric answers and show steps.)
AB: q=mcΔT=5.00×4.71×(240−210)=706.5J.
BC (if BC is fusion at 240 K): q=mΔHf=5.00×332=1660J. Total ≈2366.5J.
A student's data show temperature plateauing at 53∘C53∘C for several minutes while heating a solid. What does this plateau indicate about the substance, and how would you determine its melting point from the data?
Plateau at 53∘C53∘C indicates melting point is 53∘C53∘C.
A dilute, aqueous potassium nitrate solution—classify it as homogeneous/heterogeneous and compound/mixture and justify your classification in terms of components and uniformity.
Dilute KNO₃(aq) = homogeneous mixture (solute dissolved uniformly in solvent).
A rigid container holds a gas at 150 kPa and 27°C. What is the pressure of the gas at 127°C?
27°C = 300 K
127°C = 400 K
P₂ = 200 kPa
A 100.0‑gram sample of H₂O at 22.0∘C22.0∘C absorbs 8360 J8360 J. Using c=4.18 J/g⋅Kc=4.18 J/g⋅K, find the final temperature. Show all steps and justify whether any phase changes occur.
Use q=mcΔTq=mcΔT: ΔT=qmc=8360(100.0)(4.18)≈20.0∘CΔT=mcq=(100.0)(4.18)8360≈20.0∘C so final ≈42.0∘C≈42.0∘C (check phase: no phase change because final <100°C).
A 250‑gram sample of a substance has a boiling point of 120∘C and a heat of vaporization of 2.10×103 J/g. If heat is supplied at a constant rate of 1250 J/min, calculate the time (in minutes and seconds) required to completely vaporize the sample once it reaches the boiling point. Show the formula and all steps.
Time=420min
Using the terms melting, boiling, freezing, condensation, what phase changes use the heat of vaporization equation and heat of fusion equation? Then, explain what specific phase change is occurring with each of these four terms.
Heat of vaporization: Boiling (l-g)/condensation (g-l).
Heat of fusion: Melting (s-l) /freezing (l-s).
Provide a particle‑diagram description (text only) of a sample that is (a) a pure compound, (b) a homogeneous mixture, and (c) a heterogeneous mixture. For each, state what students should look for in a drawn diagram.
(a) pure compound: all particles identical molecules bonded in same arrangement; (b) homogeneous mixture: different molecule types uniformly distributed; (c) heterogeneous: distinct regions or clusters of different components.