45.0 14) Calculate the constant external pressure of 1.5 mmtL·m-101 a. +5.3 1J b

Question

45.0 14) Calculate the constant external pressure of 1.5 mmtL·m-101 a. +5.3 1J b. +3.0 kJ work eneny, w, gained or lost by the system 5.3 15) Ir 4.89 g of ZaCl2 is dissolved solution? in enough water to give a total volume of 500 ml, what is the molarity of the a. 0.217M b. 1.33 M 0.0179 M d. 0.849 M 0.0717M 16) Give the complete fonic equation for the reaction (if any) that occurs when aqueous solutions of Iithiunm b. 2Li+(ag) + S2-rag) + Cu2+fag) + 2 NOS-faq) CuS(s) + 2 Li+(aq) + 2 NO3-(aq) e No reaction occurs and copper (II) nitrate are mixed. Determine the oxidizing agent in the following reaction. Ni(s) + 2 AgCIO4(ag) Ni(C04)2(aq) + 2 Ag(s) d. e. Ni(s) This is not an oxidation-reduction reaction. 18) How much heat is absorbed when 45.00 g of C(o) reacts in the presence of esxcess S0zfe to produce CS2f0 and COe) according to the following chemical equation? a. 2158 k b. 239.9 kJ c. 898.5 kJ d. 179.8 kJ 19) Energy that is associated with the relative positions of electrons and nuclei in atoms and molecules is called a. gravitational energy b. thermal energy c. chemical energy. d. kinetic energy 20) For a process at constant pressure, 49,600 calories of heat are released. This quantity of heat is equivalent t [I cal-4.18J a. +1.19x 104 J b, 1.24 ×104 J

Explanation / Answer

14) Calculate the work energy, w, gained or lost by the system when a gas expands from 15 L to 35 L against a constant external pressure of 1.5 atm. 1 L. atm = 101.4 J]

Work (W) = pressure * change in volume

Therefore in this case,

Pressure is 1.5 atm

change in volume is 35-15 = 20 L

W = 1.5 atm * (35-15) L

            = 30 L . atm

            = 30 * 101.4 J

W         = 3042 J = 3.042 KJ

Here the volume is expanding, which means the work is against the environment, therefore work energy would be negative.

Finally, the answer is -3.0 KJ

15)If 4.89 g of ZnCl2 is dissolved in enough water to give a total volume of 500 mL, what is the molarity of the solution?

Molarity is equal to the number of moles of solute divided by the volume of solution measured in litres.

Molarity = moles of solute / solution in litre

In this case, moles of solute is not given, so first, we have to calculate the moles of solute from given mass (4.89 g) of ZnCl2. We multiply 4.49 g ZnCl2 with the factor of 1 mole ZnCl2 over the molar of ZnCl2, which is 136.3 g. Therefore,

4.89 g ZnCl2 * 1 mole ZnCl2 / 136.3 g ZnCl2 = 0.03588 mole

And after, from the moles we can calculate the molarity.

Molarity = 0.03588 mole ZnCl2 / 0.5 L

                    = 0.07176 M

Thus, the answer is 0.0717 M

16) Give the complete ionic equation for the reaction that occurs when aqueous solutions of lithium sulfide and copper(II)nitrate are mixed

According to solubility rules,

Rule1: Salt containing Groups I elements such as Li+, Na+, K+ are soluble in nature. Here we have group I containing salt Li2S, therefore it is soluble and exists as 2Li+ and S2- in solution.

Rule2: Nitrate ion NO3-salts are generally soluble. In this case, Cu(NO3)2 is soluble and the copper is in +2 oxidation state.

Rule3: Normally, the sulphides of the transition metals are insoluble.

If we consider different options,

Option a: The reaction dos not obey the Rule 1 and 3, Sulphides of metals are insoluble and nitrate salts are soluble.

Option b: This particular reaction obeys Rule 1 and 3 that CuS is insoluble (forms precipitate) and LiNO3 is soluble. Therefore, option 2 is correct.

Option c and d: both are wrong, because both oxidation state of copper and stoichiometry reaction are wrong.

17) Determine the oxidizing agent in the following reaction.

Ni(s) + 2 AgClO4(aq) -- > Ni(ClO4)2(aq) + 2 Ag(s)

Generally, the oxidizing agent is, itself getting reduced in a reaction, for example oxidation number moves from higher to lower (+2 to +1 or +1 to 0 or +2 to 0 etc). Meanwhile, reducing agent gets oxidized from lower oxidation number to higher.

In this reaction, from left to right,

Ni has 0 oxidation state, and after the reaction, Ni is oxidized to +2 and at the same time Ag+ (from left) moves to 0 oxidation state (right side).

Therefore, Ag+(aq) is the oxidizing agent.

18) How much heat is absorbed when 45.00 g of C(s) reacts in the presence of excess SO2(g) to produce

CS2(l) and CO(g) according to the following chemical equation?

The positive delta H represents the reaction tis endothermic which means heat energy is absorbed by the system because the products having a greater enthalpy than the reactants.

First, find the moles of 45.0 C involved in the reaction

45.0 g C * 1 mole/ 12.01 g mass of C = 3.747 moles

Second step, using the coefficients and heat to determine the absorbed energy

3.747 mol / 5 mol C = X / 239.9 KJ

X         =          239.9 KJ * 3.747 mol / 5 mol

The absorbed energy (the answer) is = 179.78 KJ

19) Energy that is associated with the relative positions of electrons and nuclei in atoms and molecules is called:

a: gravitational energy: This energy associated with gravity or potential energy hold by an object

b: thermal energy: this energy related with kinetic energy, which means due to the motion of atoms or molecules raise the temperature called thermal energy.

c: chemical energy: This energy is associated with relative portion of electrons and nuclei in atoms and molecule

d: kinetic energy : the energy associate with motion of a particle or an object

Therefore the answer is option: c

20) For a process at constant pressure, 49,600 calories of heat are released. This quantity of heat is equivalent?

49,600 calories * 4.184 J / 1 calorie = 2.0752 X 10^5 J

The answer is 2.0752 X 10^5 J

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