Q: A student mixes 50.0 mL of 1.00 M HCl with 50.0 mL of 1.00 M NaOH in a coffee-cup calorimeter. The temperature rises from 22.0$$^\circC to 28.0$^\circC. $$Assuming the density and specific heat capacity are the same as water, calculate $$q_p$$ for the reaction. ($$c = 4.184\ \text{J/g K}$$, $$\rho = 1.00\ \text{g/mL})$$

$$q_p = +2.51 \times 10^3$\ \text{J}$$

Question 1

A chemical reaction is carried out at constant pressure and releases 150 kJ of heat to the surroundings. Which of the following statements is correct about the enthalpy change ($$\Delta H) $$and the type of reaction?

Accepted Answer

$$\Delta H is $$negative; the reaction is exothermic.

Question 2

Calculate the work done (in kJ) by the system when 3.00 mol of an ideal gas is compressed from 30.0 L to 10.0 L at a constant external pressure of 1.00 atm. ($$1\ 	ext{atm} \cdot 	ext{L} = 101.3\ 	ext{J})$$

Accepted Answer

$$w = +2.02\ 	ext{kJ}$$

Question 3

Which of the following processes is associated with a positive value of $$q ($$heat absorbed by the system)?

Accepted Answer

A reaction in a beaker causes the temperature of the beaker to decrease.

Question 4

A student mixes 50.0 mL of 1.00 M HCl with 50.0 mL of 1.00 M NaOH in a coffee-cup calorimeter. The temperature rises from 22.0$$^\circC to 28.0$^\circC. $$Assuming the density and specific heat capacity are the same as water, calculate $$q_p$$ for the reaction. ($$c = 4.184\ 	ext{J/g K}$$, $$ho = 1.00\ 	ext{g/mL})$$

Accepted Answer

$$q_p = +2.51 	imes 10^3$\ 	ext{J}$$

Question 5

Which of the following best describes the main insight from Planck's quantum hypothesis?

Accepted Answer

Energy is emitted or absorbed in discrete packets called quanta, with energy $$E = n h 
u.$$

Question 6

A photon has an energy of $$4.00 	imes 10$$^{-19}$$ J. What is its wavelength in nm? (h = 6.63$$ 	imes $$10^{-34} J$$·s, $$c = 3.00 	imes 10^8$ m/s)

Accepted Answer

$$\lambda = 332\ 	ext{nm}$$

Question 7

Which of the following transitions in a hydrogen atom would result in the emission of a photon?

Accepted Answer

$$n = 4 to$$ $$n = 2$$

Question 8

In the two-slit experiment with electrons, what is the most significant observation?

Accepted Answer

Electrons create an interference pattern when many single-electron events are accumulated.

Question 9

Calculate the enthalpy change ($$\Delta H) $$for the reaction: $$2	ext{CO}(g) + 	ext{O}_2(g) ightarrow 2	ext{CO}_2(g)$$, given $$\Delta H_f^\circ$$ values: $$	ext{CO}(g) = -110.5 kJ/$$mol, $$	ext{CO}_2(g) = -393.5 kJ/$$mol$.

Accepted Answer

$$\Delta H = -566\ 	ext{kJ}$$

Question 10

Which of the following statements about Bohr's model of the hydrogen atom is correct?

Accepted Answer

Bohr assumed that the energy of each photon emitted equals the difference between two energy levels with different $$n$$ values.

Question 11

A sample of dry ice ($$	ext{CO}_2(s)) $$sublimes at constant pressure in a piston. What are the signs of $$q$$ and $$w$$ for the system?

Accepted Answer

$$q is $$positive, $$w is $$negative.

Question 12

Which of the following processes is endothermic?

Accepted Answer

Melting of ice at 0$$^\circC.$$

Question 13

Arrange the following photons in order of increasing energy: 700 nm, 500 nm, 400 nm.

Accepted Answer

700 nm \u003c 500 nm \u003c 400 nm

Question 14

What is the wavelength of light emitted when a hydrogen atom relaxes from $$n = 3 to$$ $$n = 2$$? ($$R_H = 1.097 	imes 10^7$\ 	ext{m}^{-1})$$

Accepted Answer

$$\lambda = 656\ 	ext{nm}$$

Question 15

A reaction has $$\Delta H = +75 kJ $$and $$\Delta S = +200 J/K. At $$what temperature (in K) does the reaction become spontaneous? ($$\Delta G = \Delta H - T\Delta S)$$

Accepted Answer

$$T \u003e 375\ 	ext{K}$$

Question 16

Which of the following best describes the energy change when O$$_2$$ forms from separated oxygen atoms?

Accepted Answer

Energy is released; $$\Delta H is $$negative.

Question 17

Which of the following is a correct application of Hess's Law?

Accepted Answer

The enthalpy change for a reaction is the sum of the enthalpy changes for individual steps.

Question 18

Which of the following transitions in the hydrogen atom corresponds to the absorption of the highest energy photon?

Accepted Answer

$$n = 1 to$$ $$n = 2$$

Question 19

A reaction is carried out in a rigid, sealed container. Which of the following is true about the work done by the system?

Accepted Answer

No work is done ($$w = 0) $$because $$\Delta V = 0.$$

General Chemistry II Exam 2 Study Guide: Thermochemistry & Quantum Theory

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