Chem exam 2
The actual yield of a reaction X⟶Y is 2.8gY and the percent yield of the reaction is 57.1%. What is the theoretical yield of the reaction? Your answer should have two significant figures.
%yield = (practical yield / theoretical yield)*100 Given, practical yield = 2.8g , %yield = 57.1% So, Theoretical yield = (2.8×100) / 57.1 = 4.9 g Thus theoretical yield = 4.9 g of Y.
When n=2 , what are the allowed values of l?
0,1 The values of l are restricted to 0 to n−1 by integer values. Since n=2, l=0,1.
Complete the chemical equation for the formation of hydrogen fluoride, HF(g). Remember fractional coefficients are possible when balancing equations for the purpose of determining heat of formation.
1/2 h2(G) + 1/2F2 (g) --->HF(g)
Which wavelength of light has the smallest (lowest) frequency?
10 km The relationship between wavelength (λ) and frequency (ν) can be expressed as c=2.998×108m/s=λ×ν where c = speed of light in a vacuum. Since their product is a constant, wavelength and frequency are inversely related (the longest wavelength has the smallest/lowest frequency).
What is the stoichiometric factor between N2 and NO in the following balanced chemical equation? N2+O2⟶2NO
1:2
What is the ground state electron configuration of B?
1s22s22p1 Boron has 5 electrons. Using the periodic table to fill in these 5 electrons in lowest-energy ordering (according to the Aufbau principle), the ground state electron configuration is 1s22s22p1.
In the equation A+B⟶A++B− , which species is oxidized?
A - Oxidation occurs when a molecule or ion loses electrons. A goes from a 0 charge to a 1+ charge, so it must lose an electron. Therefore, A is oxidized
Which of the following sulfate compounds will be soluble in water? Select all that apply: aluminum sulfate ammonium sulfate magnesium sulfate potassium sulfate
ALL
What is a strong acid?
An acid that efficiently transfers protons to water molecules. A strong acid is one that dissociates completely in water. This means that a strong acid efficiently transfers a proton to water molecules.
Which is a hydrogen-like species?
B4+ A hydrogen-like species is a species with a single electron (like the hydrogen atom). This includes species such as He+, Li2+, Be3+, B4+, etc.
Recall that heat capacity, C, is the ratio of heat to the change in temperature.C=qΔTSubstitute in the known values and solve.
C=6.22J4.09∘C=1.521J∘CThe answer should have three significant figures, so round to 1.52J∘C.
From the following balanced equation, 4NH3(g)+5O2(g)⟶4NO(g)+6H2O(g) how many grams ofH2Ocan be formed when6.12gNH3reacts with3.78gO2? Your answer should have three significant figures. (Round your answer to the second decimal place).
Calculate the grams of H2O formed from each reactant. 6.12gNH3×1molNH317.03gNH3×6molH2O4molNH3×18.02gH2O1molH2O=9.71gH2O 3.78gO2×1molO232.00gO2×6molH2O5molO2×18.02gH2O1molH2O=2.55gH2O Only2.55gH2Ocan be formed before the limiting reactant runs out. Notice that coefficients in stoichiometric equations (indicating numbers of moles) are exact, so they do not constrain the number of significant figures.
Which is the orbital diagram for carbon?
Carbon has the following electron configuration: C:1s22s22p2 Following Hund's rule, electrons fill orbitals singly until pairing is required. The two electrons in the 2p will be in separate orbitals, in order to maximize the number of unpaired electrons.
Which is a soluble compound? Select the correct answer below: (NH4)2SO4 BaSO4 CaSO4 Ag2SO4
Compounds containing the sulfate ion (SO2−4) are generally soluble, except when the cation is Ag+, Ba2+, Ca2+, Hg2+2, Pb2+, or Sr2+. Compounds containing these cations are insoluble.
What is true about energy? Select the correct answer below: Energy is the ability to do work or supply heat. Energy cannot convert between different forms. Energy can be created and destroyed. Energy is only found in laboratory experiments.
Energy is the ability to do work or supply heat.
Which of the following ions has the smallest radius? Select the correct answer below: F− Cl− Br− I−
F- : for ions belonging to the same group, ionic radius increases as the number of shells of electrons, n, increases. Since F is in period 2, its ion has the smallest size.
Fill in the blanks for the coefficients in the balanced version of the following equation: X2+Y2⟶XY3
First, write the unbalanced equation: X2+Y2⟶XY3 To balance X , add 2 in front of XY3. X2+Y2⟶2XY3 To balance Y , add 3 in front of Y2. 1X2+3Y2⟶2XY3 The equation is balanced.
According to the Heisenberg's uncertainty principle, a(n) _______ in the precision of measuring position results in a(n) _______ in the precision of measuring momentum. (Select all that apply
Increase, decrease decrease, increase An increase in the precision of measuring position of a particle leads to a decrease in the precision of measuring the momentum of the particle because measuring one requires a change in the other.
Which is a state function? Select the correct answer below: Internal energy Heat Work Distance
Internal energy is a state function. The value of a state function depends only on the state of a system at a given time, and not on how that state is reached. If a quantity is not a state function, then its value does depend on how the state is reached.
Which scientist determined that white light was made up of the individual colors of the rainbow combined together?
Isaac Newton Isaac Newton performed experiments with lenses and prisms and was able to demonstrate that white light consists of the individual colors of the rainbow combined together.
Which of the following elements has the largest value of IE2
Li The value of the second ionization energy, IE2, will be largest when this process removes core electrons instead of only valence electrons, since core electrons are more tightly held to the nucleus. Since Li only has 1 valence electron, its IE2 value will be much larger.
Identify the oxidizing agent in the following redox reaction CH4+2O2⟶CO2+2H2O
O2 The oxidizing agent gets reduced (oxidation number decreases, meaning it gets more negative). The oxidation number of carbon increases from −4 in CH4 to +4 in CO2. The oxidation number of oxygen decreases from 0 in O2 to −2 in CO2 and H2O. The oxidation number of hydrogen is unchanged +1 in both CH4 and H2O. This means the oxidizing agent (substance that gets reduced) is O2.
What was Bohr able to calculate with his equation?
Orbit energies of the electron Using various constants, including Planck's constant, Bohr was able to calculate the orbit energy of the electron. He got excellent agreement with Rydberg's accepted constant.
A 50.0g block of Al(cAl=0.897Jg∘C) at an initial temperature of 318∘C is placed into 50.0g of H2O(cH2O=4.184Jg∘C) at an initial temperature of 25.0∘C. What will be the final temperature of the system? Report your answer using three signficant figures.
Recall that the First Law of Thermodynamics demands that the total internal energy of an isolated system must remain constant. Any amount of energy lost by the metal must be gained by the water. Therefore, heat given off by the metal = −heat taken in by water, or: −qAl=qwater The equation used to calculate the quantity of heat energy exchanged in this process is: −qAl=−cAl mAl ΔTAl=cwater mwater ΔTwater=qwater Heat stops flowing when the two samples are at the same temperature, so same final temperature of the water will be the final temperature of the metal as well. Substitute in the known values for the equation above and rearrange to solve for Tf. −(0.897Jg∘C)(50.0 g)(Tf−318.0∘C)=(4.184Jg∘C)(50.0 g)(Tf−25.0∘C) Simplify by multiplying specific heat and mass. −(44.85J∘C)(Tf−318.0∘C)=(209.2J∘C)(Tf−25.0∘C) Simplify by multiplying heat capacity by temperature. −(44.85Tf J∘C)+14,262 J =(209.2TfJ∘C)−5,230 J Combine like terms. −254.05TfJ∘C=−19,492 J Tf=76.73∘C The answer should have three significant figures so round to 76.7∘C.
When 8.11g of a hydrocarbon is burned in a bomb calorimeter, the temperature increases by 3.75∘C. If the heat capacity of the calorimeter is 58.9J∘C and it is submerged in 742mL of water, how much heat (in kJ) was produced by the hydrocarbon combustion?
Since density of water is 1 g/mL and volume is 742 mL, mass of water = 742 g Q = Ccal*delta T + m(water)*C(water)*delta T = 58.9*3.75 + 742*4.184*3.75 = 220.875 + 11642 = 11863 J = 11.9 KJ Since this is heat released, Q is negative Answer: -11.9 KJ
When 5.82g of H2 reacts with excess Cl2 by the following equation, 533kJ of heat are produced. What is the enthalpy change of the reaction, per mole of hydrogen gas? H2+Cl2⟶2HCl
Since heat is being produced, the forward reaction is exothermic. Therefore, the ΔH for the balanced reaction is −533kJ . First, convert the mass of H2 to moles: 5.82 g H2(1.00 mol2.016 g)=2.887 mol H2 Next, convert the moles of H2 to kilojoules per mole of H2 using the ΔH given for the balanced reaction: ΔH=qrxnnH2=−533kJ2.887molH2=−184.62kJ/molH2 The answer should have three significant figures, so round to −185 kJmolH2.
Calculate the ΔH∘reaction for 4NH3(g)+5O2(g)⟶4NO(g)+6H2O(g) given ΔH∘f(NH3)=−46.19kJ/molΔH∘f(NO)=90.37kJ/molΔH∘f(H2O)=−241.82kJ/mol.
Since the heats of formation are given and we know that ΔH∘f(O2)=0kJ/mol since it is an element in its standard form, the equation ΔH∘reaction=∑n×ΔH∘f, products−∑n×ΔH∘f, reactants can be used to calculate ΔH∘reaction ΔH∘reaction=[4×(90.37 kJ/mol)+(6×(−241.82 kJ/mol)]−[4×(−46.19 kJ/mol)+5×(0kJ/mol)]=361.48 kJ/mol+(−1450.92 kJ/mol)−(−184.76 kJ/mol)−(0kJ/mol)=−904.7 kJ/mol
From the following balanced equation, 2C8H18(l)+25O2(g)⟶16CO2(g)+18H2O(g) how many grams ofH2Ocan be formed from0.996gC8H18? Your answer should have three significant figures.
The coefficients in the balanced chemical equation can be used as the stoichiometric factor between C8H18 and H2O. Molar mass converts between grams and moles. 0.996gC8H18×1molC8H18114.232gC8H18×18molH2O2molC8H18×18.015gH2O1molH2O=1.41gH2O Notice that coefficients in stoichiometric equations (indicating numbers of moles) are exact, so they do not constrain the number of significant figures.
From the following balanced equation, 4NH3(g)+5O2(g)⟶4NO(g)+6H2O(g) how many moles of H2O can be formed from 3.78mol O2?
The coefficients in the balanced chemical equation can be used as the stoichiometric factor between O2 and H2O. 3.78molO2×6molH2O5molO2=4.54molH2O
What is different between a "hot" object and a "cold" object?
The molecules in the "hot" object have a higher average kinetic energy than the molecules in the "cold" object. The particles in a "hot" object have a higher average kinetic energy compared to the particles in a "cold" object, due to the faster motion of the particles in the "hot" object. To reach thermal equilibrium, the "hot" object would transfer heat energy to the "cold" object.
What subshell is described by the quantum numbers n=2 and l=1?
The principal quantum number n describes the energy level and the value of l describes the subshell, where l=0 is an s subshell, l=1 is a p subshell, l=2 is a d subshell, and l=3 is an f subshell. Since n=2 and l=1, the subshell is 2p.
What does the spin quantum number, ms, describe? Select the correct answer below: The energy level of the orbital. The shape of the orbital. The orientation in space of the orbital. The spin of the electron.
The spin of the electron. The spin quantum number, ms, describes the spin of the electron within an orbital.
What is the wavelength of a baseball that has a mass of 145g and a velocity of 25.0ms? Use 6.626×10−34kg m2s for Planck's constant. Your answer should include three significant figures.
To find the wavelength (λ), we must use the expression: λ=hmv where h = Planck's constant (6.626×10−34kg m2s), m = mass, and v = velocity.We are given the mass and the velocity in the question. Mass is 145 g and velocity is 25.0ms. Velocity has the appropriate units, but mass is in grams instead of kilograms. This means we must convert the mass, and so 145 g=0.145 kg. Now we can plug in the values and solve for λ: λ=6.626×10−34kg m2s(0.145 kg×25.0ms)=1.83×10−34 m
Silicon has an atomic number of 14. Which of the following is the correct electron configuration for silicon according to the Aufbau principle?
Use the following diagram as needed to determine the energy ordering of each subshell, and fill the configuration from lowest energy to highest. Remember that each s subshell can hold 2 electrons, each p subshell can hold 3 electrons, etc. The first subshell is 1s, which can hold 2 electrons, so start by writing 1s2, and then determine where the remaining 14−2=12 electrons go. 1s2 The next subshell is 2s which also only holds 2 electrons. 1s22s2 The next two subshells are 2p and 3s, which can hold 6 electrons and 2 electrons, respectively. 1s22s22p63s2 At this point, 12 electrons have been accounted for, so only 2 more should be placed in the next subshell, which is the 3p subshell. 1s22s22p63s23p2
A reaction in which heat is absorbed is which of the following?
endothermic The term endothermic reaction describes the process in which the system absorbs heat from its surroundings.
