January 2012 Chemistry Regents #41-50

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AnswerLinkExplanations

41 Which equation represents a change that results in an increase in disorder?

(1 ) I2(s)=>I2(g)

(2) CO2(g) =>CO2(s)

(3) 2Na(s) + Cl2(g) =>2NaCl(s)

(4) 2H2(g) + O2(g) => 2H2O(l)

1link 

entropy  S<L<G

42 A solution consists of 0.50 mole of CaCl2 dissolved in 100. grams of H20 at 25°C. Compared to the boiling point and freezing point of 100. grams of H20 at standard pressure. the solution at standard pressure has

(1) a lower boiling point and a lower freezing point

(2) a lower boiling point and a higher freezing point

(3) a higher boiling point and a lower freezing point

(4) a higher boiling point and a higher freezing point

3link 

boiling point elevation freezing point depression

43 Given the balanced ionic equation representing a reaction:

2A1(s) + 3Cu2+(aq) ==>2A13+(aq) + 3Cu(s)

Which half-reaction represents the reduction that occurs?

(I ) Al  ==> Al3+ + 3e-

(2) Al3+ + 3e- ==>Al

(3) Cu  ==> Cu2+ + 2e-

(4) Cu2+ + 2e-  ==>Cu

4

link

 

charge goes down

electrons are on the more positive side

44 Given the equation and potential energy diagram representing a reaction:

If each interval on the axis labeled "Potential Energy (kJ/mol)" represents 10. kJ/mol, what is the heat of reaction?

(1) +60. kJ/mol         (2) +20. kJ/mol

(3) +30. kJ/mol         (4) +40. kJ/mol

3linkheat of reaction=products (C)- reactants (A+B)

50-20= +30

 

 

45 Some solid KNO3 remains at the bottom of a stoppered flask containing a saturated KNO3(aq) solution at 22°C, Which statement explains why the contents of the fl ask are at equilibrium?

(1) The rate of dissolving is equal to the rate of crystallizaion,

(2) The rate of dissolving  is greater than the rate of crystallization .

(3) The concentration of the solid is equal to the concentration of the solution.

(4) The concentration of the solid is greater than the concentration of the solution.

1

link

 

this solution is saturated

saturated is at equilibrium so rates dissolving equals rates crystallizing

 

 

46 Which formula represents the product of the addition reaction between ethene and chlorine Cl2?

 		1link

 

CH2=CH2 + Cl2 → ClCH2-CH2Cl

47 Based on Reference Table J. which two reactants react spontaneously?

(I) Mg(s) + ZnCl2 (aq)

(2) Cu(s) + FeSO4(aq)

(3) Pb(s) + ZnCl2(aq)

(4) Co(s)+ NaCl(aq)

1linkcompare the 2 metals on Table J

if the metal that is alone is higher it will react

 

48 When the pH value of a solution is changed from 2 to 1, the concentration of hydronium ions

(1) decreases by a factor of 2

(2) increases by a factor of 2

(3) decreases by a factor of 10

(4) increases by a factor of 10

3link 

each pH change is a 10 fold change in concentration of H3O+ 

Lower=decrease

Higher =increase

49 Given the balanced equation representing a nuclear reaction:

Which phrase identifies and describes this reaction?

(1) fission, mass converted to energy

(2) fission, energy converted to mass

(3) fusion, mass converted to energy

(4) fusion, energy converted to mass

3link

 

fusion of hydrogen, energy comes from mass

E=mc2

50 Given the equation representing a reversible reaction:

NH3(g) + H2O(l) <=> NH4+(aq) + OH-(aq)

According to one acid-base theory, the reactant that donates an H+ ion in the forward reaction is

(1) NH3(g)          (2) H2O(l)

(3) NH4+(aq)          (4) OH-(aq)

2link 

look at which reactant has 1 less H as a product

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