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A class traces the expansion of the universe backward in time. Which description best matches the earliest state proposed by the Big Bang Theory?
A. Cold, widely separated galaxies
B. Hot, extremely dense matter and energy
C. A mature universe filled with heavy elements
D. A static collection of fully formed stars
B. Hot, extremely dense matter and energy
Democritus and Aristotle disagreed about matter. Which statement describes Democritus' view?
A. Matter is continuous and made of four elements
B. Matter consists of tiny particles called atomos
C. Matter contains electrons embedded in positive charge
D. Matter has a dense nucleus surrounded by energy levels
B. Matter consists of tiny particles called atomo
Most alpha particles passed through the gold foil, while a few were strongly deflected. Which
conclusion best explains both observations?
A. The atom is solid, with charge spread evenly
B. The atom is mostly empty space with a small, dense nucleus
C. Electrons occupy fixed levels inside the nucleus
D. Positive and negative charges have equal masses
B. The atom is mostly empty space with a small, dense nucleus
Which statement correctly describes a catalyst?
A. It raises activation energy and is consumed
B. It increases product mass beyond the reactant mass
C. It changes the identity of the reaction products
D. It lowers activation energy and is not permanently used up
D. It lowers activation energy and is not permanently used up
Why do manufacturers determine the limiting reactant before scaling up a reaction?
A. To predict product amount and reduce unused materials
B. To guarantee that every reactant is left over
C. To avoid balancing the chemical equation
D. To increase the atomic numbers of the products
A. To predict product amount and reduce unused materials
Astronomers find that more distant galaxies generally move away faster. Which evidence for the Big Bang does this observation represent?
A. Red shift and the expanding universe
B. Formation of elements by radioactive decay
C. Fixed electron energy levels
D. Conservation of mass in reactions
Correct answer: A. Red shift and the expanding universe
Which development most directly showed that Dalton's solid, indivisible atom model was
incomplete?
A. The discovery of the electron
B. The observation of red shift
C. The balancing of chemical equations
D. The formation of helium after the Big Bang
A. The discovery of the electron
According to collision theory, a collision produces a reaction only when the particles:
A. have sufficient energy and the correct orientation
B. have equal masses and opposite charges
C. collide at low speed in any orientation
D. are both present in excess quantities
A. have sufficient energy and the correct orientation
In a reaction mixture, one reactant is completely consumed and production stops although another
reactant remains. The consumed reactant is the:
A. catalyst
B. excess reactant
C. limiting reactant
D. theoretical product
C. limiting reactant
Identify the reactant that remains after the limiting reactant has been completely consumed.
Correct answer: Excess reactant
A faint, nearly uniform microwave signal is detected from every direction in space. What does this signal represent?
A. Light emitted by nearby planets
B. Remnant energy from the early universe
C. Energy released only by supernovae
D. Radiation produced by Earth's atmospher
B. Remnant energy from the early universe
In Thomson's model, negatively charged electrons were pictured as:
A. embedded in a positively charged sphere
B. concentrated with protons in a tiny nucleus
C. moving only between electron clouds
D. forming a solid, indivisible particle
A. embedded in a positively charged sphere
Powdered calcium carbonate reacts faster than equal-mass marble chips under the same conditions. What best explains the difference?
B. Powder exposes more surface area for collisions.
Identify the numbers written before chemical formulas to show reacting and product mole ratios.
Stoichiometric coefficients
Identify the process in which light atomic nuclei combine inside stars to form heavier nuclei
Nuclear fusion
Balance the combustion equation using the smallest whole-number coefficients:
___ C4H10 + ___ O2 -> ___ CO2 + ___ H2O
Correct answer: 2C4H10 + 13O2 -> 8CO2 + 10H2O
Why must the equation H2 + O2 -> H2O be balanced before using it in calculations?
A. To show equal numbers of each type of atom on both sides
B. To make oxygen the limiting reactant
C. To show that all reactions occur at the same rate
D. To change the molar masses of the substances
A. To show equal numbers of each type of atom on both sides
Two reactants are tested separately to calculate how much product each could form. How is the
limiting reactant identified?
A. It produces the larger calculated amount of product
B. It has the greater initial mass
C. It produces the smaller calculated amount of product
D. It has the smaller molar mass
Correct answer: C. It produces the smaller calculated amount of product
For N2 + 3H2 -> 2NH3, which mole relationship is correct?
A. 1 mol N2 reacts with 2 mol H2
B. 1 mol N2 produces 3 mol NH3
C. 3 mol H2 produces 2 mol NH3
D. 2 mol N2 reacts with 1 mol H2
C. 3 mol H2 produces 2 mol NH3
Mole-to-mole: For 2KClO3 -> 2KCl + 3O2, how many moles of O2 form when 8.0 mol KClO3 decomposes completely?
Correct answer: 12 mol O2. Calculation: 8.0 mol KClO3 x (3 mol O2 / 2 mol KClO3) = 12 mol O2.
Limiting reactant: N2 + 3H2 -> 2NH3. If 3.2 mol N2 reacts with 5.4 mol H2, identify the limiting reactant and calculate the moles of NH3 produced.
Correct answer: H2 is the limiting reactant; 3.6 mol NH3 forms. Calculation: 5.4 mol H2 x (2 mol NH3 / 3 mol H2) = 3.6 mol NH3
Two reactants are tested separately to calculate how much product each could form. How is the
limiting reactant identified?
A. It produces the larger calculated amount of product
B. It has the greater initial mass
C. It produces the smaller calculated amount of product
D. It has the smaller molar mass
C. It produces the smaller calculated amount of product.
Mass-to-mass: NH4NO3 -> N2O + 2H2O. If 45.7 g NH4NO3 decomposes, what mass of N2O forms?
Use 80.06 g/mol for NH4NO3 and 44.02 g/mol for N2O
Correct answer: 25.1 g N2O. Calculation: 45.7 g x (1 mol / 80.06 g) x (1 mol N2O / 1 mol NH4NO3) x (44.02 g / 1 mol) = 25.1 g.