Chemistry Answers

True or False

1. Thermodynamics is the scientific study of the interconversion of heat and other kinds of energy. True or false?

2. A thermodynamic system, which in the case of chemistry is a reaction, with the sorroundings being in a closed system. True or false?

3. The first law of thermodynamics states that energy cannot be created not destroyed, that means that energy is constant. True or false?

4. During a chemical reaction, the energy of the system remains the same as bonds in reactant are broken and the atoms rearrange to form the new bonds of the products. True or false?

5. We can think of the first law of thermodynamics as an energy balance sheet, much like a money balance sheet kept in a bank that does currency exchange. True or false?

To analyze the alcohol content of a wine, a chemist needs 1.00 L of an aqueous 0.200 M K2Cr2O7 (potassium dichromate) solution. How much solid K2Cr2O7 must be weighted out to make this solution?

Describe also the laboratory procedures that the chemist must employ in preparing K2Cr2O7 solution.

9.Given the equation and 𝐻 values(see standard enthalpy of formation f of various 𝑓

∆𝐻°

compounds table given in the discussion ) What is the heat of reaction at 298 K for the reaction:

C(s) + 2 H2(g) CH4(g)

a. -74.8 kJ c. 278 kJ

b. -27.6 kJ d. 296 kJ

10. Knowing the enthalpy of the reaction in number 9, the reaction is:

a. endothermic c. either a or b

b. exothermic d. cannot be determined

8. Given the following equation, CH4(g) + 2O2(g) → CO2(g) + H2O (l)

What is the heat of reaction (kJ) at 298 K for the reaction: (see standard enthalpy of formation

∆𝐻°f of various compounds table given in the discussion )

a. -890. 3 kJ c. 493.3 kJ

b. -393.5 kJ d. 593.2 kJ

5. Zero is the equivalent standard enthalpy formation of;

a. more stable allotropes c. less stable allotropes

b. the reactant of greater concentration d. the reactant of less concentration

6. Which of the following has a standard heat of formation that is NOT equal to zero,

a. Na b. CO2 c. Fe d. Br2

7. Which of the following is NOT TRUE about Hess’s Law?

a. If an equation is reversed the sign of the ∆𝐻 is retained.

b. It is used to find heat changes in either physical or chemical changes

c. It makes possible to measure a heat of reaction without actually doing the experiment

d. It says that if you add two or more thermochemical equations to give a final equation, you

can also add the heats of reaction to give the final heat of reaction.

1. The first law of thermodynamics which states that energy cannot be created or destroyed but could be converted to from one form to another.

a. Law of multiple proportion

c. Law of conservation of mass

b. Law of definite proportion

d. Law of conservation of energy

3. Which of the following describes what happens when you hold an ice cube in your hand?

a. Heat flows from the ice to your hand, melting of ice is exothermic

b. heat flows from the ice to your hand, melting of ice is endothermic

c. heat flows from your hand to the ice, melting of ice is exothermic

d. heat flows from your hand to the ice, melting of ice is endothermic

4. Baking of cookies is

a. endothermic c. either a or b

b. exothermic d. cannot be determined

5. What is the ∆𝐸 for a gas that releases 43 J of heat and has 120 J of work done on it.

a. 55 J b. 77 J c. 99 J d. 110 J

1. What physical and chemical changes in our everyday life that are obviously accompanied by energy change? Give three examples.

2. How do heat and work affect a system?

What is the steric number for germanium disulfide?

In an experiment,1.90g of NH3 reacts with 4.96g of O2.

4NH3+5O2~4NO+6H2O

(i) which is the limiting reactant? Show your working.

(ii) How many grams of excess reactant remain? Show your working.

(III) How many grams of NO is formed? Show your working.

1.An organic compound is known to be nonvolatile and non electrolyte.A 0.35-g sample is dissolved in water and diluted to 150mL.The osmotic pressure is measured as 0.04 atm at 25°C.The approxulmate mass number for this compound is 1400g/mol.From the data provided in this problem and knowing that the density of the solution is 1.00g/mL.

a.Calculate the freezing point of the solutions.

b.Determine if the freezing point change would be a good way to determine the molecular mass of the compound.

c.Would the boiling point change be a better determining factor than the freezing point change?