Answers26-27 - C - RUSD Chemistry in the Earth SystemThe Energy of Chemical Reactions

The Energy of Chemical Reactions — Test Answers

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1
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Which letter represents the activated complex?

A
cap b
B
cap g
C
cap f
D
cap A
2
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Consider these intermediate chemical equations. cap c times s plus 1 half cap o sub 2 g rightarrow CO times g CO times g plus 1 half cap o sub 2 g rightarrow CO sub 2 times g When you form the final chemical equation, what should you do with CO ?

A
Write CO as a reactant and a product in the final chemical reaction.
B
Cancel out CO because it appears as a reactant in one intermediate reaction and a product in the other intermediate reaction.
C
Add the two CO molecules together, and write them as reactants in the final chemical reaction.
D
Write CO only once as a reactant in the final chemical reaction.
3

A sample of iron Fe with a mass of 200.0g releases 9 comma 840 cal when it freezes at its freezing point. What is the molar heat of fusion for iron? Use q is equal to n triangle cap h

A
3 comma 280 point 0 cal over mol
B
2 comma 771 point 8 cal over mol
C
2 comma 811 point 7 cal over mol
D
2 comma 747 point 7 cal over mol
4

Ammonia, NH sub 3 , Δ⁢H_f=−46.2kJ reacts with oxygen to produce water Δ⁢H_f=−241.8kJ and nitric oxide, NO , Δ⁢H_f=91.3kJ , in the reaction: 4 NH sub 3 g plus 5 cap o sub 2 g rightarrow 6 cap h sub 2 cap o g plus 4 NO g What is the enthalpy change for this reaction? Use Δ⁢H_rxn=∑(Δ⁢H_f_1p⁢r⁢o⁢d⁢u⁢c⁢t⁢s)−∑(Δ⁢H_f_1r⁢e⁢a⁢c⁢tan⁡t⁢s)

A
900 point 8 kJ
B
negative 900 point 8 kJ
C
104 point 6 kJ
D
negative 104 point 6 kJ
5

Which is the most important factor in determining the state of a substance?

A
the position of the electrons on the outer valence shells
B
the number of molecules in a substance
C
the size of the atoms in a substance
D
the balance between intermolecular forces and kinetic energy
6

Which describes the enthalpy change associated with an endothermic reaction?

A
It is negative because the enthalpy of the reactants is greater than the enthalpy of the products.
B
It is positive because the enthalpy of the products is greater than the enthalpy of the reactants.
C
It is negative because the enthalpy of the products is greater than the enthalpy of the reactants.
D
It is positive because the enthalpy of the reactants is greater than the enthalpy of the products.
7

Consider the rate law. cap r is equal to k times open bracket NO sub 2 close bracket squared What happens to the rate if the concentration is tripled?

A
The rate decreases by a factor of 6 .
B
The rate increases by a factor of 9 .
C
The rate doubles.
D
The rate triples.
8

Find the enthalpy of hydration for an iodide ion in the process RbI rightarrow Rb raised to the plus plus cap i raised to the negative power power Use triangle cap h sub sol is equal to negative triangle cap h sub lat plus triangle cap h sub hydr triangle cap h sub sol is equal to 31 point 0 kJ/mol triangle cap h sub lat is equal to negative 630 point 0 kJ/mol triangle cap h sub hydr Rb raised to the plus power is equal to negative 315 point 0 KJ/mol of Rb raised to the plus power is equal to negative 315 point 0 kJ/mol

A
negative 661 point 0 kJ/mol
B
negative 661 kJ/mol
C
negative 284 point 0 kJ/mol
D
negative 284 kJ/mol
9

A reaction occurs when solid X is placed into solution Y. As a result, the temperature of the new solution increases by 3 times degree C The temperature rises another 2 times degree C when more of solid X is added to the solution. What does this indicate about the effect of adding more solid?

A
It decreased the number of molecular collisions.
B
It decreased the space between the molecules and lowered the reaction rate.
C
It increased the space between the molecules and increased the reaction rate.
D
It increased the number of molecular collisions.
10

cap h sub 2 cap o has a triangle cap h sub vap is equal to 40 point 7 kJ over mol What is the quantity of heat that is released when 27 point 9 g of cap h sub 2 cap o condenses? Use q is equal to n triangle cap h

A
60 point 0 0 kJ
B
61 point 0 5 kJ
C
63 point 0 9 kJ
D
68 point 6 0 kJ
11

Which statement about enthalpy is true?

A
Enthalpy is a state function because its change depends only on initial and final conditions.
B
The enthalpy of formation for a pure element in its standard state is always positive.
C
Enthalpy is not a state function because its change depends on the identities of the reactants and products.
D
The enthalpy of formation for a pure element in its standard state is always negative.
13

Consider LiBr rightarrow Li raised to the plus plus Br raised to the negative power power and these information. triangle cap h sub lat is equal to negative 803 kJ/mol triangle cap h sub hydr of Br to the th power is not equal to negative 284 kJ/mol triangle cap h sub sol is equal to negative 47 kJ/mol What is the triangle cap h sub hydr of Li raised to the plus power ? Use triangle cap h sub sol is equal to negative triangle cap h sub lat plus triangle cap h sub hydr

A
470 kJ/mol
B
negative 570 kJ/mol
C
472 kJ/mol
D
negative 566 kJ/mol
14

Which statement best describes why industry uses heterogeneous catalysts?

A
They cause stronger bonds to form between molecules.
B
They tend to be more stable.
C
They are all gases at room temperature.
D
They form strong bonds with reactant molecules.
15

Consider these intermediate chemical equations. cap c times s plus cap o sub 2 times g rightarrow CO sub 2 times g triangle cap h sub 1 is equal to negative 393 point 5 kJ 2 CO g plus cap o sub 2 times g rightarrow 2 CO sub 2 g triangle cap h sub 2 is equal to negative 566 point 0 kJ 2 cap h sub 2 cap o g rightarrow 2 cap h sub 2 g plus cap o sub 2 times g triangle cap h sub 3 is equal to 483 point 6 kJ The overall chemical equation is C(s)+H_2​O(g)→CO(g)+H_2​(g) To calculate the final enthalpy of the overall chemical equation, which step must occur?

A
Multiply the first equation by three, and triple the enthalpy. Then, add.
B
Reverse the first equation, and change the sign of the enthalpy. Then, add.
C
Divide the third equation by two, and double the enthalpy. Then, add.
D
Reverse the second equation, and change the sign of the enthalpy. Then, add.
16

What happens as the activation energy increases?

A
The pressure of the system decreases.
B
The kinetic energy of colliding molecules changes.
C
The reaction begins to slow down.
D
The reactant surface area decreases.
17

Which energy changes in the enthalpy of solution are endothermic, and which are exothermic?

A
triangle cap h sub solute , triangle cap h sub solvent and triangle cap h sub mix are all is exothermic.
B
triangle cap h sub solute is exothermic; triangle cap h sub solvent and Δ⁢Hmix are endothermic.
C
triangle cap h sub solute and triangle cap h sub solvent are endothermic; triangle cap h sub mix is exothermic.
D
triangle cap h sub solute is endothermic; triangle cap h sub solvent and triangle cap h sub mix are exothermic.
18

Which statement describes a homogeneous catalyst?

A
It forms different products than the uncatalyzed reaction forms.
B
It is completely consumed by reactants.
C
It is in a gaseous phase only.
D
It is in the same phase as the reactants.
19

Which statement best describes the reaction pathway graph for an exothermic reaction but not an endothermic reaction?

A
The products are higher in energy than the reactants.
B
It has a valley in the middle that is its lowest point.
C
The reactants are higher in energy than the products.
D
It has a hill in the middle that is the highest point.
20

A student decides to use the rate law when investigating the reaction between sodium bicarbonate and vinegar. NaHCO sub 3 times s plus CH sub 3 COOH A q rightarrow Na raised to the plus A q power plus CH sub 3 COO raised to the negative A q power plus cap h sub 2 cap o l plus CO sub 2 times g Why would a student use rate laws in this investigation?

A
to find out if NaHCO sub 3 or CH sub 3 COOH is acting as a catalyst
B
to see how much sodium acetate is formed
C
to find out if more aqueous solution than gas is produced
D
to see how concentrations of NaHCO sub 3 and CH sub 3 COOH affect reaction rate
21

Which is an overall third-order reaction?

A
cap r is equal to k cap x cap y
B
cap r is equal to k cap A squared cap b
C
cap r is equal to k cap x squared cap y cubed
D
cap r is equal to k cap A cap b to the 1th power

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