States of Matter and Chemical Equilibrium Practice Quiz (29 questions)

Question 1

1. A sample consists of a single chemical constituent made of two different elements. Which description fits it?

A pure compound, such as H₂O

A mixture of simple substances

A mixture of compounds

A pure simple substance, such as O₂

Explanation

A pure substance contains one chemical constituent, which may be a compound made from multiple elements. The simple-substance choice confuses constituent count with element count, while the mixture choices incorrectly treat one constituent as several.

Answer

A pure compound, such as H₂O

Question 2

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?

Solid, liquid, or gas

A fixed state independent of conditions

Solid or liquid, but not gas

Liquid or gas, but not solid

Explanation

A pure substance can occur as a solid, liquid, or gas depending on temperature and pressure. Excluding gas or solid omits a possible state, and purity does not fix the physical state.

Answer

Solid, liquid, or gas

Question 3

3. A pure substance changes directly from a solid to a gas without becoming liquid. What is this change called?

Vaporization

Fusion

Sublimation

Condensation

Explanation

Sublimation is the transition from solid directly to gas. Vaporization is liquid to gas, condensation is gas to solid, and fusion is solid to liquid.

Answer

Sublimation

Question 4

4. At fixed pressure, a pure substance is heated through successive phase changes. Which direction of structural order should its states follow?

From more disordered toward more ordered

From more ordered toward more disordered

From gas toward liquid and then solid

Between states with unchanged ordering

Explanation

At fixed pressure, heating takes a pure substance from the more ordered state toward the more disordered state. The reverse trend and the gas-to-solid sequence describe cooling, while unchanged ordering misses the stated progression.

Answer

From more ordered toward more disordered

Question 5

5. On a pressure–temperature diagram for a pure substance, what does the triple point identify?

A boundary where solid and liquid coexist

The pressure and temperature where solid, liquid, and gas coexist

The endpoint where liquid–gas distinction disappears

A temperature at which the gas phase alone is stable

Explanation

The triple point is the specific pressure and temperature at which all three phases—solid, liquid, and gas—coexist. The critical point is the liquid–gas endpoint, and a two-phase boundary does not represent three-phase coexistence.

Answer

The pressure and temperature where solid, liquid, and gas coexist

Question 6

6. A temperature reading is $25\,^{\circ}\mathrm{C}$ . What is this temperature in kelvin using $T\,(\mathrm{K})=t\,(^{\circ}\mathrm{C})+273.15$ ?

298.15\,\mathrm{K}

298.00\,\mathrm{K}

248.15\,\mathrm{K}

25.00\,\mathrm{K}

Explanation

Add the offset to the Celsius reading: $25+273.15=298.15\,\mathrm{K}$ . The other values omit the offset, round it prematurely, or subtract it.

Answer

$$298.15\,\mathrm{K}$$

Question 7

7. A substance is taken beyond the endpoint of its liquid–gas boundary on a state diagram. What phase description applies there?

Coexisting solid, liquid, and gas phases

A homogeneous supercritical fluid

A distinct liquid phase

A distinct gas phase

Explanation

Beyond the critical point, the liquid–gas discontinuity ends and the substance is a homogeneous supercritical fluid. Distinct liquid or gas phases imply the discontinuity remains, while three-phase coexistence describes the triple point.

Answer

A homogeneous supercritical fluid

Question 8

8. A chemist selects several constituents with specified chemical identities and physical states, then encloses them with a real or imaginary closed boundary Σ. What has been defined?

A pure substance

A physicochemical system

A chemical phase

The external environment

Explanation

A physicochemical system is an assembly of constituents of defined chemical nature and physical state bounded by a real or imaginary closed surface. The external environment is outside that boundary, a chemical phase is not the full definition, and a pure substance need not be the system.

Answer

A physicochemical system

Question 9

9. A sealed vessel allows energy to pass through its walls but prevents matter from crossing them. How should the vessel’s contents be classified as a system?

An open system

A closed system

A heterogeneous system

An isolated system

Explanation

A closed system permits energy exchange but no matter exchange; an isolated system permits neither. An open system allows exchanges across its boundary, while heterogeneous describes phases rather than exchange.

Answer

A closed system

Question 10

10. Two identical containers of gas are combined, doubling the total mass and volume while leaving the temperature unchanged. Which classification correctly describes mass and temperature?

Mass is extensive; temperature is intensive

Mass is intensive; temperature is extensive

Both mass and temperature are intensive

Both mass and temperature are extensive

Explanation

Mass depends on the amount of matter and is additive across subsystems, so it is extensive; temperature is independent of amount and non-additive, so it is intensive. Calling mass intensive reverses the distinction, while the other choices misclassify temperature or both quantities.

Answer

Mass is extensive; temperature is intensive

Question 11

11. A sample of liquid water contains a separate layer of immiscible liquid, forming two distinct phases. How is the sample classified?

A single-phase system

A heterogeneous system

A pure substance

A homogeneous system

Explanation

A system containing at least two distinct phases is heterogeneous. Homogeneous and single-phase classifications require one uniform phase, and multiple constituents do not by themselves determine whether a system is a pure substance.

Answer

A heterogeneous system

Question 12

12. An ideal gas mixture occupies $0.0249\ \mathrm{m^3}$ at $100\ \mathrm{kPa}$ and $300\ \mathrm{K}$ . Using $R=8.314\ \mathrm{J\,K^{-1}\,mol^{-1}}$ , approximately how many moles are present?

0.0100 mol

0.910 mol

1.00 mol

100 mol

Explanation

From $PV=nRT$ , $n=PV/(RT)=(100000\times0.0249)/(8.314\times300)\approx1.00\ \mathrm{mol}$ . The value 0.0100 mol results from failing to convert kilopascals, 100 mol reflects an inverted relationship, and 0.910 mol is consistent with using an incorrect temperature scale.

Answer

0.50 mol·L⁻¹

Answer

$$-2, -1, +3$$

Answer

It decreases by $$0.60\ \mathrm{mol}$$.

Answer

The equilibrium extent $$\xi_e$$.

Answer

A dimensionless intensive quantity describing a constituent's behavior.

Answer

The pure solid has activity equal to one.

Answer

$$\frac{a_C}{a_Aa_B^2}$$

Answer

They have the same equilibrium constant, but their equilibrium compositions may differ.

Answer

Toward the reactants, in the reverse direction.

Answer

The equilibrium is disrupted.

Answer

The assay is a chemical method; the electrical measurement is a physical method.

Answer

$$\frac{2n}{13}$$ mol

Answer

Include nitrogen in the total as an inert gas.

Question 13

13. A gas phase contains 2 mol of nitrogen and 3 mol of oxygen. What is the mole fraction of oxygen in that phase?

0.60

1.50

0.40

0.30

Explanation

Mole fraction is the constituent amount divided by the total amount: $x_{\mathrm{O_2}}=3/(2+3)=0.60$ . The value 0.40 is the nitrogen fraction, 1.50 divides by the other constituent, and 0.30 uses an incorrect numerator or denominator.

Question 14

14. An ideal gas mixture has a total pressure of 200 kPa, and a constituent has mole fraction 0.25. What is that constituent’s partial pressure?

150 kPa

200.25 kPa

50 kPa

800 kPa

Explanation

Dalton’s law gives $p_i=x_iP$ , so $p_i=0.25\times200=50\ \mathrm{kPa}$ . The value 150 kPa uses the complementary fraction, 200.25 kPa adds unlike quantities, and 800 kPa divides instead of multiplying.

Question 15

15. A dilute preparation uses water in large excess, and 0.30 mol of a dissolved substance is present in a final solution volume of 0.60 L. What is the substance’s concentration?

0.50 mol·L⁻¹

0.50 L·mol⁻¹

2.0 mol·L⁻¹

5.0 mol·L⁻¹

Explanation

In an aqueous solution, water in large excess is the solvent and the dissolved substance is a solute; its dilute-solution concentration is $C_i=n_i/V=0.30/0.60=0.50\ \mathrm{mol\,L^{-1}}$ . The value 2.0 inverts the ratio, L·mol⁻¹ gives the wrong units, and 5.0 reflects a decimal-place error.

Question 16

16. For the reaction $2A + B \rightarrow 3C$ , which algebraic stoichiometric numbers correspond to $A$ , $B$ , and $C$ , respectively?

-3, -1, +2

+2, +1, -3

-2, +1, +3

-2, -1, +3

Explanation

Reactants have negative algebraic stoichiometric numbers and products have positive ones, with magnitudes taken from the balanced equation. The positive-reactant choice reverses the reactant signs, the mixed-sign choice gives $B$ the wrong sign, and the swapped-magnitude choice assigns the wrong coefficient to $A$ and $C$ .

Question 17

17. In a reaction, a constituent has stoichiometric number $\nu_i=-2$ and the reaction extent increases by $0.30\ \mathrm{mol}$ . By how much does the amount of that constituent change?

It decreases by

0.15\ \mathrm{mol}

.

It increases by

0.60\ \mathrm{mol}

.

It decreases by

0.60\ \mathrm{mol}

.

It decreases by

0.30\ \mathrm{mol}

.

Explanation

The amount change is $dn_i=\nu_i\,d\xi=(-2)(0.30\ \mathrm{mol})=-0.60\ \mathrm{mol}$ , so the constituent decreases by $0.60\ \mathrm{mol}$ . An increase drops the negative sign, a decrease of $0.30\ \mathrm{mol}$ ignores the coefficient, and a decrease of $0.15\ \mathrm{mol}$ uses its reciprocal.

Question 18

18. A reaction is reversible and reaches equilibrium while some reactant remains. Which extent describes its final state?

The initial extent before the reaction proceeds.

The maximum extent

\xi_{\max}

.

The extent at which the reactant is exhausted.

The equilibrium extent

\xi_e

.

Explanation

A reversible reaction ends at its equilibrium extent $\xi_e$ ; $\xi_{\max}$ describes a complete forward reaction in which the limiting reactant disappears. Reactant exhaustion and maximum extent therefore confuse equilibrium with completion, while the initial extent is not the final state.

Question 19

19. What best describes chemical activity in chemical equilibrium laws?

A dimensionless intensive quantity describing a constituent's behavior.

An extensive quantity measuring the total amount of a constituent.

A concentration value that applies in every type of phase.

A pressure value with units used directly in equilibrium laws.

Explanation

Chemical activity is a dimensionless intensive quantity used to describe a constituent's behavior in a system and appears in equilibrium laws. An extensive amount, a universal concentration, and a dimensional pressure each misstate its nature or scope.

Question 20

20. A pure ideal gas has a pressure of $2.5\ \mathrm{bar}$ . Given $P^0=1\ \mathrm{bar}$ , what is its activity?

0.40

2.5

1.0

2.5\ \mathrm{bar}

Explanation

For a pure ideal gas, $a=P/P^0$ , so $a=(2.5\ \mathrm{bar})/(1\ \mathrm{bar})=2.5$ and is dimensionless. The reciprocal gives $0.40$ , the reference pressure alone gives $1.0$ , and retaining bar incorrectly leaves the result dimensional.

Question 21

21. A reaction mixture contains a pure solid and a dissolved solute in dilute aqueous solution. Which statement about the solid's activity is correct?

The pure solid's activity varies with the amount of solid present.

The pure solid's activity equals the solute's concentration ratio.

The pure solid has activity equal to one.

The pure solid's activity depends on its concentration.

Explanation

A pure condensed phase has activity equal to one, just as the solvent does in a dilute aqueous solution; a dissolved solute instead has concentration-dependent activity. Concentration dependence and a concentration ratio misapply the solute rule, while amount dependence contradicts the pure-phase value.

Question 22

22. A solute in a dilute aqueous solution has concentration $0.20\ \mathrm{mol\,L^{-1}}$ . Given $C^0=1\ \mathrm{mol\,L^{-1}}$ , what is its activity?

5.0

1.0

0.20\ \mathrm{mol\,L^{-1}}

0.20

Explanation

For a dilute aqueous solute, $a_i=C_i/C^0$ , giving $a_i=(0.20\ \mathrm{mol\,L^{-1}})/(1\ \mathrm{mol\,L^{-1}})=0.20$ . The inverse ratio gives $5.0$ , the reference concentration alone gives $1.0$ , and the unreduced concentration is dimensional rather than an activity.

Question 23

23. For a reaction written as $A + 2B \rightleftharpoons C$ , which expression gives the dimensionless reaction quotient at time $t$ ?

\frac{a_C}{a_Aa_B^2}

\frac{a_C}{a_Aa_B}

\frac{a_Aa_B^2}{a_C}

a_C-a_A-2a_B

Explanation

The reaction quotient is the product of each activity raised to its signed stoichiometric coefficient, so products appear in the numerator and reactants in the denominator. Reversing the ratio gives the inverse quotient, omitting a power misuses the coefficient, and subtracting activities is not the quotient definition.

Question 24

24. Two preparations of the same reaction reach equilibrium at the same temperature but start with different amounts of reactants and products. Which statement is correct?

They have the same equilibrium constant, but their equilibrium compositions may differ.

They have different equilibrium constants because their initial compositions differ.

They have the same equilibrium composition, but their equilibrium constants may differ.

They have different equilibrium constants because their pressures may differ.

Explanation

The thermodynamic equilibrium constant depends only on temperature, while equilibrium composition can depend on the initial state. Different initial compositions do not change the constant, and the reaction quotient varies with the system state rather than being fixed by temperature alone.

Question 25

25. A homogeneous reaction mixture contains both reactants and products, and its current reaction quotient is greater than its equilibrium constant. In which direction will it evolve spontaneously?

Neither direction, because the system is at equilibrium.

Toward the products, in the forward direction.

Toward the products, because products are already present.

Toward the reactants, in the reverse direction.

Explanation

When $Q_r > K^0$ , the mixture has a relative excess of products and evolves in the reverse direction until the quotient reaches the equilibrium constant. The forward-direction choice reverses the comparison, while equilibrium requires equality.

Question 26

26. In a heterogeneous reaction system, a required constituent is absent from the final state. What does this indicate?

The reaction quotient must equal the equilibrium constant.

The equilibrium is disrupted.

The equilibrium constant has become independent of temperature.

The system remains at equilibrium with an unchanged composition.

Explanation

An equilibrium is disrupted when a constituent required by the reaction is no longer present in the final state. A changed concentration alone does not establish this condition, and quotient-constant equality characterizes equilibrium rather than its disruption.

Question 27

27. A laboratory determines equilibrium composition in two ways: one procedure chemically assays the amount of a reactant, while another measures an electrical signal that varies with concentration. How should the procedures be classified?

Both procedures are physical methods because they quantify the equilibrium state.

Both procedures are chemical methods because they determine composition.

The assay is a physical method; the electrical measurement is a chemical method.

The assay is a chemical method; the electrical measurement is a physical method.

Explanation

Chemical methods determine composition by assaying a reactant or product, whereas physical methods measure a physical quantity linked to concentration. The electrical signal is a concentration-dependent physical quantity, while directly assaying the reactant is chemical analysis.

Question 28

28. A closed mixture starts with equal amounts, $n$ mol each, of butane and oxygen and reacts completely according to the balanced combustion equation. What is the maximum reaction extent?

\frac{n}{13}

mol

\frac{2n}{13}

mol

\frac{13n}{2}

mol

\frac{n}{4}

mol

Explanation

Each reaction extent consumes $\frac{13}{2}$ mol of oxygen, so the initial $n$ mol of oxygen allows $\xi_m=\frac{n}{13/2}=\frac{2n}{13}$ mol; oxygen is limiting in this equimolar mixture. Choosing $\frac{n}{4}$ treats butane as limiting, while the other values misapply or invert the oxygen coefficient.

Question 29

29. A combustion calculation models air as one-fifth oxygen and four-fifths nitrogen. When determining the final total gas amount, how should the nitrogen be treated?

Include nitrogen in the total as an inert gas.

Exclude nitrogen from the total because it is inert.

Add nitrogen to the product amounts as a reaction product.

Replace the oxygen amount with the total air amount.

Explanation

The total gas amount includes every gas present, including the nitrogen supplied with air, even though nitrogen is inert in the combustion reaction. Omitting inert nitrogen confuses nonreactivity with absence, while treating air as pure oxygen or nitrogen as a product misrepresents the mixture or reaction.

States of Matter and Chemical Equilibrium Practice Quiz (29 questions)

All questions and answers

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?

3. A pure substance changes directly from a solid to a gas without becoming liquid. What is this change called?

4. At fixed pressure, a pure substance is heated through successive phase changes. Which direction of structural order should its states follow?

5. On a pressure–temperature diagram for a pure substance, what does the triple point identify?

6. A temperature reading is 25 ∘C25\,^{\circ}\mathrm{C}25∘C. What is this temperature in kelvin using T (K)=t (∘C)+273.15T\,(\mathrm{K})=t\,(^{\circ}\mathrm{C})+273.15T(K)=t(∘C)+273.15?

7. A substance is taken beyond the endpoint of its liquid–gas boundary on a state diagram. What phase description applies there?

8. A chemist selects several constituents with specified chemical identities and physical states, then encloses them with a real or imaginary closed boundary Σ. What has been defined?

9. A sealed vessel allows energy to pass through its walls but prevents matter from crossing them. How should the vessel’s contents be classified as a system?

10. Two identical containers of gas are combined, doubling the total mass and volume while leaving the temperature unchanged. Which classification correctly describes mass and temperature?

11. A sample of liquid water contains a separate layer of immiscible liquid, forming two distinct phases. How is the sample classified?

12. An ideal gas mixture occupies 0.0249 m30.0249\ \mathrm{m^3}0.0249 m3 at 100 kPa100\ \mathrm{kPa}100 kPa and 300 K300\ \mathrm{K}300 K. Using R=8.314 J K−1 mol−1R=8.314\ \mathrm{J\,K^{-1}\,mol^{-1}}R=8.314 JK−1mol−1, approximately how many moles are present?

13. A gas phase contains 2 mol of nitrogen and 3 mol of oxygen. What is the mole fraction of oxygen in that phase?

14. An ideal gas mixture has a total pressure of 200 kPa, and a constituent has mole fraction 0.25. What is that constituent’s partial pressure?

15. A dilute preparation uses water in large excess, and 0.30 mol of a dissolved substance is present in a final solution volume of 0.60 L. What is the substance’s concentration?

16. For the reaction 2A+B→3C2A + B \rightarrow 3C2A+B→3C, which algebraic stoichiometric numbers correspond to AAA, BBB, and CCC, respectively?

17. In a reaction, a constituent has stoichiometric number νi=−2\nu_i=-2νi​=−2 and the reaction extent increases by 0.30 mol0.30\ \mathrm{mol}0.30 mol. By how much does the amount of that constituent change?

18. A reaction is reversible and reaches equilibrium while some reactant remains. Which extent describes its final state?

19. What best describes chemical activity in chemical equilibrium laws?

20. A pure ideal gas has a pressure of 2.5 bar2.5\ \mathrm{bar}2.5 bar. Given P0=1 barP^0=1\ \mathrm{bar}P0=1 bar, what is its activity?

21. A reaction mixture contains a pure solid and a dissolved solute in dilute aqueous solution. Which statement about the solid's activity is correct?

22. A solute in a dilute aqueous solution has concentration 0.20 mol L−10.20\ \mathrm{mol\,L^{-1}}0.20 molL−1. Given C0=1 mol L−1C^0=1\ \mathrm{mol\,L^{-1}}C0=1 molL−1, what is its activity?

23. For a reaction written as A+2B⇌CA + 2B \rightleftharpoons CA+2B⇌C, which expression gives the dimensionless reaction quotient at time ttt?

24. Two preparations of the same reaction reach equilibrium at the same temperature but start with different amounts of reactants and products. Which statement is correct?

25. A homogeneous reaction mixture contains both reactants and products, and its current reaction quotient is greater than its equilibrium constant. In which direction will it evolve spontaneously?

26. In a heterogeneous reaction system, a required constituent is absent from the final state. What does this indicate?

27. A laboratory determines equilibrium composition in two ways: one procedure chemically assays the amount of a reactant, while another measures an electrical signal that varies with concentration. How should the procedures be classified?

28. A closed mixture starts with equal amounts, nnn mol each, of butane and oxygen and reacts completely according to the balanced combustion equation. What is the maximum reaction extent?

29. A combustion calculation models air as one-fifth oxygen and four-fifths nitrogen. When determining the final total gas amount, how should the nitrogen be treated?

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Make your own practice quizzes

6. A temperature reading is $25\,^{\circ}\mathrm{C}$ . What is this temperature in kelvin using $T\,(\mathrm{K})=t\,(^{\circ}\mathrm{C})+273.15$ ?

12. An ideal gas mixture occupies $0.0249\ \mathrm{m^3}$ at $100\ \mathrm{kPa}$ and $300\ \mathrm{K}$ . Using $R=8.314\ \mathrm{J\,K^{-1}\,mol^{-1}}$ , approximately how many moles are present?

16. For the reaction $2A + B \rightarrow 3C$ , which algebraic stoichiometric numbers correspond to $A$ , $B$ , and $C$ , respectively?

17. In a reaction, a constituent has stoichiometric number $\nu_i=-2$ and the reaction extent increases by $0.30\ \mathrm{mol}$ . By how much does the amount of that constituent change?

20. A pure ideal gas has a pressure of $2.5\ \mathrm{bar}$ . Given $P^0=1\ \mathrm{bar}$ , what is its activity?

22. A solute in a dilute aqueous solution has concentration $0.20\ \mathrm{mol\,L^{-1}}$ . Given $C^0=1\ \mathrm{mol\,L^{-1}}$ , what is its activity?

23. For a reaction written as $A + 2B \rightleftharpoons C$ , which expression gives the dimensionless reaction quotient at time $t$ ?

28. A closed mixture starts with equal amounts, $n$ mol each, of butane and oxygen and reacts completely according to the balanced combustion equation. What is the maximum reaction extent?