chemistry exam part 3
At what temperature does the solid start melting?
0°C
Which best describes the energy change that takes place during deposition?
Heat energy is released by the substance.
Why does platinum metal make a good catalytic surface for reactant molecules?
It holds reactant molecules in a good position for them to react.
Which statement best describes the use of a catalyst in a fuel cell?
It increases reaction rates.
Which catalyzed reaction breaks up ozone?
O3+O-CS->2O2
Two samples of carbon come into contact. A heat transfer will occur between sample A and sample B. What must be true for heat to transfer from sample A to sample B?
The average kinetic energy of A is greater than that of B.
AgCl(s)<-> Ag+(aq) + Cl-(aq) What will happen to the chemical equilibrium if AgNO3 is added?
The chemical equilibrium of the system shifts left
What does C represent?
enthalpy of reaction
Which kind of reaction does this graph represent?
exothermic because Hrxn = -167 kJ
The formula actual yield/ theoretical yield is used to calculate the______ of a reation
percent
What is the enthalpy of the overall chemical equation NO(g) + O(g) ->NO(g)?
-304.1 kJ
A chemical reaction has Hf,reactants = -1,023 kJ and Hf,products = -935.3 kJ. Which graph can be used to represent this reaction pathway?
-935.3 KJ and -10233 with the products higher then the reactants
N2(g)+3H2(g)<->2NH3(g) At equilibrium, the concentrations of the different species are as follows.[NH3] = 0.105 M[N2] = 1.1 M[H2] = 1.50 MWhat is the equilibrium constant for the reaction at this temperature?
0.0030
The equation represents the combustion of sucrose. C12H22O11 + 12O2-> 12CO2 + 11H2O If there are 10.0 g of sucrose and 8.0 g of oxygen, how many moles of sucrose are available for this reaction?
0.029 mol
PCl5(g)<-> PCl3(g)+Cl2(g) At 500 K, the reaction is at equilibrium with the following concentrations.[PCI5]= 0.0095 M[PCI3] = 0.020[CI2] = 0.020 MWhat is the equilibrium constant for the given reaction?
0.042
A sample of an unknown substance has a mass of 0.465 kg. If 3,000.0 J of heat is required to heat the substance from 50.0°C to 100.0°C, what is the specific heat of the substance?
0.129 J/(gi°C)
Which arrows represent the phase transitions in which heat energy is gained?
1, 2, and 3
NaCl has a delta Hfus = 30.2 kJ/mol. What is the mass of a sample of NaCl that needs 732.6 kJ of heat to melt completely?
1,417.7 g
Consider the balanced equation.2HCl + Mg ->MgCl2 + H2If 40.0 g of HCl react with an excess of magnesium metal, what is the theoretical yield of hydrogen?
1.11 g
2NOCl(g)<->2NO(g)+Cl2(g) At equilibrium, the concentrations are as follows.[NOCl] = 1.4 ´ 10-2 M[NO] = 1.2 ´ 10-3 M[Cl2] = 2.2 ´ 10-3 MWhat is the value of Keq for the reaction expressed in scientific notation?
1.6'10^-5
2HF(g)<->H2(g)+F2(g)82 x 10-2 M[H2] = 8.4 x 10-3 M[F2] = 8.4 x 10-3 MWhat is the value of Keq for the reaction expressed in scientific notation?
2.1 x 10-2
The molar heat of fusion for water is 6.01 kJ/mol. How much energy must be added to a 75.0-g block of ice at 0°C to change it to 75.0 g of liquid water at 0°C?
25.0 kJ
The chemical equation shows iron(III) phosphate reacting with sodium sulfate.2FePO4 + 3Na2SO4-> Fe2(SO4)3 + 2Na3PO4What is the theoretical yield of Fe2(SO4)3 if 20.00 g of FePO4 reacts with an excess of Na2SO4?
26.52 g
A sample of hexane (C6H14) has a mass of 0.580 g. The sample is burned in a bomb calorimeter that has a mass of 1.900 kg and a specific heat of 3.21 J/giK. What amount of heat is produced during the combustion of hexane if the temperature of the calorimeter increases by 4.542 K?
27.7 kJ
Hydrogen gas reacts rapidly with oxygen gas in the presence of a platinum catalyst. Which equation correctly represents this reaction?
2H2(g)+O2(g) -Pt->2H2O(g)
When 40.0 mL of 1.00 M H2SO4 is added to 80.0 mL of 1.00 M NaOH at 20.00°C in a coffee cup calorimeter, the temperature of the aqueous solution increases to 29.20°C. If the mass of the solution is 120.0 g and the specific heat of the calorimeter and solution is 4.184 J/g • °C, how much heat is given off in the reaction? (Ignore the mass of the calorimeter in the calculation.)
4.62 kJ
Which arrow would most likely represent the phase change that occurs when silver is poured into a mold and cools to become a solid bar?
5
The initial temperature of a bomb calorimeter is 28.50°C. When a chemist carries out a reaction in this calorimeter, its temperature decreases to 27.45°C. If the calorimeter has a mass of 1.400 kg and a specific heat of 3.52 J/(gi°C), how much heat is absorbed by the reaction?
5,170 J
Carbon monoxide (CO) reacts with hydrogen (H2) to form methane (CH4) and water (H2O). CO(g)+ 3H2(g)<-> CH4(g)+H2O(g)The reaction is at equilibrium at 1,000 K. The equilibrium constant of the reaction is 3.90. At equilibrium, the concentrations are as follows.[CO] = 0.30 M[H2] = 0.10 M[H2O] = 0.020 MWhat is the equilibrium concentration of CH4 expressed in scientific notation?
5.9x10^-2
Copper has a Hfus = 13.0 kJ/mol. What mass of copper releases 112.4 kJ of heat as it freezes?
549 g
The molar heat of vaporization for methane, CH4, is 8.53 kJ/mol. How much energy is absorbed when 54.8 g of methane vaporizes at its boiling point?
6.42 kJ
The electrolysis of water forms H2 and O2. 2H2O ->2H2 + O2 What is the percent yield of O2 if 10.2 g of O2 is produced from the decomposition of 17.0 g of H2O?
67.6%
A 115.0-g sample of oxygen was produced by heating 400.0 g of potassium chlorate. 2KClO3 ->2KCI + 3O2 What is the percent yield of oxygen in this chemical reaction?
73.40%
What is the percent yield of ferrous sulfide if the actual yield is 220.0 g and the theoretical yield is 275.6 g?
79.8%
A 13.00 g sample of citric acid reacts with an excess of baking soda as shown in the equation. H3C6H5O7+3NaHCO3 -> 3CO2+3H2O+Na3C6H5O7 What is the theoretical yield of carbon dioxide?
8.93 g
Which best explains the relationship between evaporation and temperature?
A liquid evaporates faster at higher temperatures because more particles have a higher speed and can overcome attractions in the liquid.
Loren has the samples of elements that are listed below at room temperature. He exposes the samples to the same heat source until each sample reaches a temperature of 90.0°C.10 g of Al(s) ( = 0.897 J/(gi°C))10 g of Ag(s) (= 0.234 J/gi°C )10 g of Fe(s) ( = 0.450 J/gi°C)10 g of Zn(s) ( = 0.387 J/gi°C )From first to last, which lists the order in which these samples will reach 90.0°C?
Ag,Zn,Fe,Al
How does the potential-energy diagram for a reaction indicate whether the reaction is endothermic or exothermic?
An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.
Which statement about exothermic reactions is accurate?
As reactants form products, the potential energy decreases.
Which statement correctly describes a reaction in dynamic equilibrium?
At dynamic equilibrium, the reactions continue but the amounts of reactants and products do not change.
Which line indicates a higher reaction rate?
B because it has a lower activation energy.
Which reaction is exothermic?
CH4 + 2O2 CO2 + 2H2O + 891 kJ
What is the correct enthalpy diagram using the Hess law for this system?
CH4(g)+2O2(g) -802kJ -890kJ CO2(g)+2H2O(g) -88kJ CO2(g)+2H2O(l)
Consider the following intermediate chemical equations. CH4(g)+ 2O2(g)-> CO2(g) +2H2O(g) 2H2O(g)->2H2O(l) Which overall chemical equation is obtained by combining these intermediate equations?
CH4(g)+2O2(g)->CO2(g)+2H2O(l)
Which statement describes a catalyst?
Catalysts provide a lower energy pathway for the reaction.
A chemist wants to calculate the amount of heat that is absorbed by a sample of copper as it is melted. Which constant should she use?
Delta H of fussion
Which can be used to determine the delta H?
E and D
Which inference is supported by evidence in the graph?
E and D show that the energy of the products is less than that of the reactants.
Which reaction is an example of heterogeneous catalysis?
Ethene gas reacts with hydrogen gas by using a nickel catalyst.
The specific heat of water is 4.18 J/(gi°C) and that of wood is 1.97 J/(gi°C). Which statement is correct?
Given equal masses, water will heat up less than wood if the same heat is added.
Which statement defines activation energy?
It is the difference between reactant energy and maximum energy.
Consider the statement below."When nitrogen is liquefied, heat is released."Is this statement true or false?
It is true because heat is released when a gas changes to a liquid.
What overall effect does adding a catalyst have on a chemical reaction?
It lowers the activation energy that is needed.
Which statement accurately describes this graph?
It represents an exothermic reaction because the reactants have more energy than the products.
According to Le Chatelier's principle, what always happens to the equilibrium of a reaction when the temperature is reduced?
It shifts to the left.
COCl2(g)<->CO(g) + Cl2(g) Which is the correct equation for K?
K=[CO][Cl2]/[COCl2]
aA+bB<->cC+dD What is the equilibrium constant expression for the given system?
Keq= [C]^c[D]^d/[A]^a[B]^b
Which represents the correct equilibrium constant expression for the reaction below? Cu(s)+2Ag+(aq)<->Cu2+(aq)+2Ag(s)
Keq=[Cu2+]/[Ag+]^2
2H2O(g)<->2H2(g)+O2(g) What is the equilibrium constant expression for the given system?
Keq=[H2]^2[O2]/[H2O]^2
H2SO4(aq) <->2H+(aq) + SO42-(aq) The addition of which compound will cause a shift in equilibrium because of a common ion effect?
MgSO4
Which will cause an increase in the reaction rate between molecules?
Molecules collide more frequently.
A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot?
Molecules in the cake are moving faster than molecules in the skin.
How should the enthalpy of an intermediate step be manipulated when used to produce an overall chemical equation?
Multiply the enthalpy by -1 if the chemical equation is reversed.
The second reaction in the formation of sulfuric acid occurs slowly. 2So2(g) +O2(g)-> 2SO3(g)NO2 is added to the reaction to speed it up. In which form would this substance be a homogeneous catalyst for this reaction?
NO2(g)
Consider the combustion reaction for acetylene. 2C2H2(l) + 5O2(g)-> 4CO2(g) + 2H2O(g) If the acetylene tank contains 37.0 mol of C2H2 and the oxygen tank contains 81.0 mol of O2, what is the limiting reactant for this reaction?
O2
What is the final chemical equation from the following intermediate chemical equations? P4O6(s)->P4(s)+3O2(g) P4(s)+5O2(g)-> P4O10(s)
P4O6(s)+2O2(g)->P4O10(s)
Consider the following intermediate chemical equations. 2P(s)+ 3Cl2(g) -> 2PCl3(l) PCl3(l)+ Cl2(g)-> PCl5(s) When you combine the intermediate chemical equations, which substance do you cancel out?
PCl3
Which applies to the collision theory?
Particles need to collide in order to react.
The production of water proceeds according to the following equation.2H2(g) + O2(g) ->2H2O(g)Which describes a way to speed up the collisions between hydrogen and oxygen molecules to produce more water?
Place the reactants in a smaller container.
N2(g)+O2(g)-> 2NO(g) 2NO(g) +O2(g)->2NO2(g) Which best describes what Jason should do with the oxygen molecules?
Place two of them as products
During an endothermic phase change, what happens to the potential energy and the kinetic energy?
Potential energy increases, and kinetic energy stays the same.
Why are enzymes required for living things to function?
Reactions take place too slowly at body temperature and must be speeded up.
Which statement best describes why specific heat capacity is often more useful than heat capacity for scientists when comparing two materials?
Specific heat capacity is an intensive property and does not depend on sample size.
A hot metal plate at 150°C has been placed in air at room temperature. Which event would most likely take place over the next few minutes?
The air molecules that are surrounding the metal will speed up, and the molecules in the metal will slow down.
The temperature of a gas is increased. Which statement best explains the effect that this has on the motion of gas particles?
The average kinetic energy increases, and the particles collide more frequently.
CH3COOH<->CH3COO-(aq) + H+(aq) What will happen to the chemical equilibrium if MgCl2 is added?
The chemical equilibrium of the system will be unaffected.
2H2(g) + O2(g)<->2H2O(g) What will happen if the pressure of the system is increased?
The forward reaction will be favored.
Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?
The gas molecules in both containers have the same average kinetic energy.
Which statement describes how this graph would change if the reaction could be made to go faster?
The hill would be shorter.
The temperature of a sample of liquid water changes from 50°C to 30°C. Which statement best explains the change that must happen at the molecular level?
The molecules move more slowly and their average kinetic energy decreases.
Which of the following statements is true?
The overall chemical reaction is exothermic.
N2(g)+ 3H2(g)<-> 2NH3(g)Which statement is true for the equilibrium system?
The rate of the forward reaction equals the rate of the reverse reaction.
Consider the reaction below. 2NH3(g) <-> N2(g)+3H2(g) What is the most likely effect to the forward reaction if there is an increase in pressure on this reaction?
The reaction rate decreases.
Which statement best describes this graph?
This is an endothermic reaction with a positive delta Hrxn.
As tempeture decreases the heat lost increases in the graph Which explanation correctly describes the phase change in the graph?
This is an exothermic reaction that involves freezing.
Which statement defines calorimeter?
a device that measures the heat that is gained or lost in a chemical change
What scientific tool would be the most helpful when measuring the temperature of a substance that is undergoing a phase change?
a thermometer
What is the definition of a common ion as it applies to Le Chatelier's principle?
an ion that is present in an equilibrium system and a compound added to the system
When does carbon dioxide absorb the most heat energy?
during sublimation
In what type of reaction or process does heat flow into the system?
endothermic
What does D represent?
energy of the products
Consider the reaction H2(g) + I2(g) HI(g) with an equilibrium constant of 46.3 and a reaction quotient of 525. Which direction will the system shift to?
equilibrium will shift to the left to favor the reactants.
Jean has a sample of a liquid. If she changes the liquid's phase by _____________ it, the molecules will spread out, allowing the sample to expand and fill a container of any shape or volume.
evaporating
What would be the greatest difference in using an open ceramic coffee mug rather than an insulated mug with a lid as a calorimeter?
exchange of energy with the surroundings
H2O is initially present in a state where its molecules are far apart. During a change of state, its molecules slow down. Which change of state has most likely taken place?
from a gas to a liquid
Which term is used to describe the amount of heat that is required to melt 1 mol of a substance?
heat of fusion
An increase in temperature affects the reaction rate by
increasing the number of molecules that have sufficient kinetic energy to react.
The final overall chemical equation is CaO(s)+CO2(g)-> CaCO3(s). When the enthalpy of this overall chemical equation is calculated, the enthalpy of the second intermediate equation
is halved and has its sign changed.
When two intermediate chemical equations are combined, the same substance that appears in the same phase can be canceled out, provided that
it is a reactant in one intermediate reaction and a product in the other reaction.
What is used up in and stops a chemical reaction?
limiting reactant
The heat capacity of a sample should be divided by which quantity to find the specific heat capacity?
mass in grams
A change in which factor will affect the rate of reaction only when gases are involved?
pressure
Ben observes how quickly some dry wood is burning in a campfire. Which term best relates to Ben's observation?
reaction rate
According to Le Chatelier's principle, a system in chemical equilibrium responds to stress by shifting the equilibrium in a direction that
reduces the stress.
In which phase transition do molecules move directly from a state involving vibration of particles in a fixed position to a state involving random movement of high-speed particles?
sublimation
Magnesium oxide does not readily decompose into magnesium and oxygen. The reaction is shown below.MgO(s) + 601.7 kJ ->Mg(s) + ½O2(g)Which factor plays the most important role in allowing this reaction to occur?
temperature
What does this piece of evidence best support?
the Maxwell-Boltzmann distribution
Reactions cannot occur without a certain minimum amount of energy. What is this minimum amount of energy called?
the activation energy
Which scientific tool is the most useful when trying to convert a known amount of grams of water to moles of water?
the periodic table
aA(aq) + bB(aq) cC(aq) + dD(aq) According to Le Chatelier's principle, which statement correctly completes the table below? Change Effect on equilibrium constant (K) Increase in concentration of products Value of K does not change Increase in temperature Value of K also changes Increase in pressure ?
value of K does not change