What defines a pure substance?
It contains a single chemical constituent.
What distinguishes a simple pure substance from a compound pure substance?
A simple substance, such as O₂, contrasts with a compound such as H₂O.
What three states can a pure substance occupy?
Solid, liquid, or gas.
What is the state change from solid directly to gas called?
Sublimation.
At fixed pressure, how does heating a pure substance change its order?
It moves from a more ordered state toward a more disordered state.
What is the triple point of a pure substance?
The pressure and temperature at which its solid, liquid, and gas phases coexist.
How is Celsius temperature converted to kelvin?
What marks the critical point on a liquid–gas phase diagram?
The end of the liquid–gas discontinuity.
What defines a physicochemical system?
An assembly of constituents of defined chemical nature and physical state, bounded by a real or imaginary closed surface Σ.
What exchanges can an open system permit?
Matter and energy exchange.
What exchanges can a closed system permit?
Energy exchange but no matter exchange.
How do intensive parameters depend on matter and combine across subsystems?
They are independent of the amount of matter and non-additive.
How do extensive parameters depend on matter and combine across subsystems?
They depend on the amount of matter and are additive.
How many uniform phases does a homogeneous system have?
One uniform phase.
What equation relates pressure, volume, amount, and temperature in an ideal gas mixture?
What is the gas constant in joules per kelvin per mole?
How is constituent ’s mole fraction calculated?
What do mole fractions sum to within a single phase?
One.
How is constituent ’s partial pressure calculated in an ideal gas mixture?
What defines an aqueous solution?
Water is the solvent in large excess, and dissolved solutes are present.
What does a stoichiometric coefficient specify in a balanced reaction equation?
The amount ratio of a reactant or product.
What sign does a stoichiometric coefficient have for a reactant?
Negative.
How does the amount of constituent depend on reaction extent ?
What is the differential change in constituent 's amount during a reaction?
At what extent does the limiting reactant disappear in a complete forward reaction?
At the maximum extent, .
What is chemical activity?
A dimensionless intensive quantity describing a constituent’s behavior and used in equilibrium laws.
What is the activity formula for a pure ideal gas?
What is the standard pressure for ideal-gas activity?
What is the activity of a pure condensed phase?
One.
What is the activity of the solvent in a dilute aqueous solution?
One.
What is the activity formula for a solute in a dilute aqueous solution?
How is the dimensionless reaction quotient defined for a reaction written as ?
.
What does the thermodynamic equilibrium constant depend on?
Temperature only.
What evolution occurs when in a homogeneous system with reactants and products present?
Forward evolution.
When is a chemical equilibrium considered disrupted?
When a required constituent is absent from the final state.
How do chemical methods determine equilibrium composition?
They assay a reactant or product.
How do physical methods determine equilibrium composition?
They measure a physical quantity linked to concentration.
How are the entities arranged in a solid?
They are compact and ordered.
How are entities arranged in a liquid and in a gas?
Liquid entities remain in contact but are disordered; gas entities are disordered and dispersed.
At fixed pressure, what determines a pure substance’s state-change temperature?
The selected pressure fixes the change temperature.
At what pressure does water’s triple point occur?
6 mbar.
What is the slope sign of water’s fusion curve?
Negative.
What is water’s critical pressure?
221 bar.
What can supercritical water dissolve that enables proposed pollutant extraction?
Organic and ionic compounds and large amounts of oxygen.
What kinds of changes can occur within a system?
Physical state changes, chemical rearrangements of matter, or transformations of an atomic nucleus.
What remains constant in a closed system despite compositional change?
Its mass.
How is an ideal gas mixture’s density relative to air calculated?
, with molar masses in g·mol⁻¹.
How is the mass fraction of constituent calculated in a homogeneous liquid mixture?
What equation does a reaction satisfy when written with algebraic stoichiometric numbers?
How is the conversion fraction of reactant defined?
The amount consumed divided by its initial amount.
How is the volumetric reaction extent defined?
What is the activity formula for constituent in an ideal gas mixture?
What does represent in the ideal-gas mixture activity formula?
The partial pressure of constituent .
Which pure solvent is omitted from a reaction-quotient expression?
A pure solvent with activity one.
How does heating affect an endothermic reaction’s equilibrium constant?
It increases the equilibrium constant.
What defines the inversion temperature ?
The temperature at which the equilibrium constant equals one.
In which direction can a reaction proceed when only reactants are initially present?
Only in the forward direction.
What does a very large indicate about a forward reaction?
It is nearly complete.
What happens to AgCl after dissolving mol in 1 L of water?
It dissolves completely, disrupting the equilibrium.
What condition defines equivalence for a monoprotic acid titrated with a standard monobase?
What is the acidity constant for the acid–base pair AH/A⁻?
What is Kohlrausch's law for conductivity in dilute aqueous solutions?
What formula gives pH in dilute aqueous solutions?
What is the balanced equation for butane combustion?
What limits an equimolar mixture of butane and oxygen, and what is its maximum extent?
Oxygen is limiting, and .
How is conversion fraction defined for a stoichiometric butane–oxygen mixture?
.
What is the water mole fraction at half-reaction in stoichiometric butane combustion?
0.30.
How is air modeled, and what must be included when calculating total gas amount?
Air is one-fifth O₂ and four-fifths N₂, and the nitrogen must be included.
At 550 K, what equilibrium conversion and mole fractions result for PCl₃ + Cl₂ ⇌ PCl₅?
The conversion is 0.12; PCl₃ and Cl₂ are each 46.8%, and PCl₅ is 6.4%.
For SO₂ oxidation at 800 K, what residual SO₂ amount and partial pressure follow from the near-complete-reaction approximation?
The residual amount is mol, with a partial pressure of bar.
At the inversion temperature, which direction does ammonia synthesis proceed for the stated mixture at 500 bar?
Forward, since .
What are the different crystalline solid forms of a pure substance called?
Polymorphs.
Answer 29 questions on States of Matter and Chemical Equilibrium.
1. A sample consists of a single chemical constituent made of two different elements. Which description fits it?
2. A sealed sample of a pure substance is observed at different temperatures and pressures. Which set of physical states may it occupy under suitable conditions?
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