Question

____ 1. To conduct an experiment, a scientist places a small piece of aluminum in a test tube and adds sodium hydroxide solution. Bubbles of gas are produced and the outside of the test tube becomes hot to the touch. Which of the following is true?

1. The reaction is endothermic, and the system gains energy from the surroundings.

2. The reaction is exothermic, and the system loses energy to the surroundings.

3. The reaction is endothermic, and the system loses energy to the surroundings.

4. The reaction is exothermic, and the system gains energy from the surroundings.

____ 2. The magnitude of the potential energy in a change differs according to what type of change occurs. What is the order from lowest potential energy change to highest potential energy change?

1. nuclear change, chemical change, phase change

2. chemical change, phase change, nuclear change

3. phase change, chemical change, nuclear change

4. phase change, nuclear change, chemical change

____ 3. A chemical reaction is carried out in a coffee cup calorimeter. The temperature of the water changes from 25.2 °C to 19.8 °C. Which statement is correct?

1. The water loses energy, so the reaction is exothermic.

2. The water gains energy, so the reaction is exothermic.

3. The water loses energy, so the reaction is endothermic.

4. The water gains energy, so the reaction is endothermic.

____ 4. Methanol is an important industrial solvent. To produce methanol, carbon monoxide and hydrogen gas are reacted together:

CO(g) + 2 H2(g)------->CH3OH(l)

Use bond energies to estimate the enthalpy of this reaction.

Bond	Average bond energy (kJ/mol)
O–H	467
O–O	146
O=O	495
C–C	347
C=C	614
C–O	358
C=O	745
C=O	1072
C–H	413
C–Cl	339
C–F	485
H–CL	427
H–F	565
F–F	154
H–H	432

a. 266 kJ/mol

b. –455 kJ/mol

c. –128 kJ/mol

d. 4000 kJ/mol

Answer 1

1) Answer is the reaction is Exothermic and system loses energy to the surrounding. Because test tube is hot from outside hence heat is released and process is Exothermic.

2) Answer is phase change, chemical change and nuclear change. Phase change has least energy and nuclear change has most.

3) Answer is the water loses energy, so the reaction is Endothermic. Since, temperature of water decreases hence it loses energy and reaction is Endothermic.

4) Answer is c).

∆H = ∆H(bond breaked) - ∆H (bond formed)

= - 3∆H(C-H) - ∆H(C-O) - ∆H(O-H) + 2∆H(H-H) + ∆H(CO)

= -3(413) - 358 - 467 + 2(432) + 1072

= -1239 - 358 - 467 + 864 + 1072

= -128