Chemistry Exam #3

The heat of reaction of one of the following reactions is the average bond energy for the N-H bond in NH3. Which one?

(1/3)NH3(g) ---> (1/3)N(g) + H2(g)

Which response includes all the following changes that represent an increase in entropy and no others? (1) the freezing of water (2) the condensation of steam (3) the sublimation (vaporization) of dry ice, solid CO2 (4) the separation of salts and pure water from seawater

(3)

Which one of the following reactions has a positive entropy change?

2NH4NO3(s) --> 2N2(g) + 4H2O(g) + O2(g)

Which statement is incorrect?

A process that absorbs energy from its surroundings is called exothermic.

Given the energy diagram below, the reaction

Absorbs energy

Which of the following statements regarding spontaneous changes is false?

All exothermic reactions are spontaneous.

A flask containing helium gas is released into a closed room. Which of the following ideas regarding energy is FALSE?

All these statements are true.

A process occurs spontaneously and deltaS < 0. Which statement below must be true?

Both (a) and (b) are correct.

Which statement about the dispersal of matter and energy is FALSE?

Dispersal of matter results in a more ordered system.

Which of the following is not a formation reaction?

H2O(l) + SO3(l) ---> H2SO4(l)

Which of the following statements about the first law of thermodynamics and energy is false?

Kinetic energy cannot be converted to potential energy.

Which one of the following substances is in its standard state?

Na(s)

Consider the reaction below at 25C for which deltaS = 16.1 J/K. CH4(g) + N2(g) + 163.8 kJ --> HCN(g) + NH3(g) Which one of the following statements describes the reaction?

Spontaneous at relatively high temperatures only.

Which term is NOT correctly matched?

State function - property dependent on how the process takes place

Which of the following statements regarding the third law of thermodynamics is incorrect?

The absolute S at 298K can be positive or negative.

Which statement regarding enthalpy change is incorrect?

The absolute enthalpy of a system can be experimentally measured.

Which statement below is FALSE?

The entropy of a system increases when order increases.

Which physical change listed below would have a negative value of deltaS?

The formation of dew on grass.

The enthalpy change of a process is defined by

The quantity of heat transferred in or out of a system as it undergoes a change at constant pressure.

Consider the following equation carefully, and determine the sign of deltaS for the reaction it describes. NH4Br(s) + NH3(g) + HBr(g) deltaH = +188.3 kJ

The reaction is spontaneous only at relatively high temperatures.

Which of the following techniques cannot be used to calculate deltaH rxn?

Using melting points of reactants and products

The following reaction is spontaneous only below 5000K. What conclusions can be drawn regarding this reaction? A + B ---> AB

deltaH is negative and deltaS is negative.

Joseph Priestly prepared oxygen by heating mercury(II) oxide. The compound HgO is stable at room temperature but decomposes into its elements (Hg and O2) at high temperatures. What conclusions can be drawn concerning deltaH and deltaS for this decomposition reaction?

deltaH is positive and deltaS is positive.