CHEMISTRY REACTIONS AND ENERGY SOPHIA LEARNING
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Temperature is a measure of an object’s ________.
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potential energy
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mechanical energy
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work
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kinetic energy
CONCEPT
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
Which of these is NOT an instrument for measuring radiation?
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Geiger counter
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dosimeters
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galvanometer
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scintillation counter
CONCEPT
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
When you balance the equation C₂H₆ + O₂ —> CO₂ + H₂O, what is the coefficient of oxygen?
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2
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7
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6
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4
RATIONALE
There are two carbons on the left but only one on the right, and the carbon is in a single chemical species on each side. Put a 2 in front of the CO₂ on the right hand side. Because the oxygen is in two compounds on the right, we will look at the hydrogen next as it is in one compound on each side of the equation. There are six hydrogens on the left and two on the right – put a 3 in front of the H₂O on the right. Now we have two oxygens on the left and seven on the right. Put a 3.5 in front of the O₂ on the left. To express everything in whole numbers, multiply every coefficient on both sides by two, and the equation is balanced.
CONCEPT
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
Which of these is a common radioactive tracer used in medicine?
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carbon-14
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technetium-99
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radon-222
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uranium-236
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
What is the age of mummified primate skin that contains 8.25% of the original quantity of C-14?
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2.06 x 10⁴ y
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473 y
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2 y
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1.21 x 10⁴ y
RATIONALE
Carbon-14 has a half-life of 5730 y. Determine the decay constant and then the age of the skin: λ = 0.693/5730 y = 1.21 x 10⁻⁴ y⁻¹. Then, ln (1.00 / 0.0825) = (1.21 x 10⁻⁴)t, and t = 2.495 / 1.21 x 10⁻⁴ = 2.06 x 10⁴ y
CONCEPT
“Rusting” is a process that involves iron reacting with which of these chemicals?
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nitrogen
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hydrogen
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carbon dioxide
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oxygen
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
The entities in a nuclear reaction that consist of high-energy electrons are known as ________.
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positrons
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beta particles
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alpha particles
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gamma rays
The value of the entropy change for the process H₂O (l) –> H₂O (s) is ________.
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positive
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zero
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unchanged
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negative
RATIONALE
The process is a phase transition from liquid to solid, thus a net decrease in (negative) dispersal of matter.
CONCEPT
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
2HF (aq) + Zn (s) –> ZnF₂ (s) + H₂ (g) would be best classified as which type of reaction?
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combustion
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acid-base
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precipitation
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single displacement
RATIONALE
Here an ion in solution (H⁺) is displaced via the oxidation of a metallic element (Zn). So this is a single displacement reaction.
CONCEPT
When ΔH < 0, the reaction is considered to be ________.
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exothermic
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combustion
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endothermic
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expansion
CONCEPT
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
If 23.6 g of hydrogen gas reacts with 28.3 g of nitrogen gas, what is the maximum amount of product (ammonia, NH₃) that can be produced?
[N₂ + 3H₂ –> 2NH₃; N = 14.0 g/mol, H = 1.01 g/mol]
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68.8 g
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34.4 g
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23.6 g
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133 g
RATIONALE
First, write the balanced chemical equation. Then, convert g hydrogen and g nitrogen to moles of each using their molar masses, and use the stoichiometric ratio from the balanced equation to convert each mole value to moles of product. Whichever produces the least amount of product is the limiting reactant.
CONCEPT
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
What is the molar mass of K₂CO₃?
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106 g/mol
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138 g/mol
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6 g/mol
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99 g/mol
RATIONALE
Potassium carbonate is made of 2 atoms of potassium, 1 atom of carbon, and 3 atoms of oxygen. To calculate the molar mass, you need to add up all the individual atoms’ molar masses to get the molecule’s molar mass: (2 x 39.1 g/mol) + (1 x 12.0 g/mol) + (3 x 16.0 g/mol) = 138 g/mol
CONCEPT
To answer this question, you may need access to the periodic table of elements, a calculator, and the equations and charts in the tutorial associated with this question.
C-14 decays into N-14 and what other particle?
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proton
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beta particle
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electron
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alpha particle
A piece of unknown substance has a mass of 437.2 g and requires 8460 J to increase its temperature from 19.3 °C to 68.9 °C.
Assuming the substance is one of those listed in the table presented in this lesson, what is the identity of the substance?
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iron
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aluminum
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lead
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copper
RATIONALE
To determine the identity of the substance from the table, you need to determine its specific heat (c). Rearranging the equation q = cmΔT gives c = q/(mΔT) = 8460 J / [437.2 g (68.9 – 19.3] °C) = 0.390 J/g °C. According to the data in the table, copper seems to be a likely candidate.
CONCEPT
A fission chain reaction can be controlled and sustained in a ________.
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beaker
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nuclear reactor
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calorimeter
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turbine
CONCEPT
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