A geological sample is found to have a Pb-206/U-238 mass ratio of 0.337/1.00

1) A geological sample is found to have a Pb-206/U-238 mass ratio of 0.337/1.00. Assuming there was no Pb-206 present when the sample was formed, how old is it? The half-life of U-238 is 4.5 × 109 years.

A. 2.1 × 109 years

B. 1.4 × 1010 years

C. 2.4 × 1010 years

D. 7.1 × 109 years

E. 7.3 × 1011 years

Answer; A. 2.1 × 109 years

2) A sample initially contains 8.0 moles of a radioactive isotope. How much of the sample remains after five half-lives? Express your answer using two significant figures.

3)The nuclide 6Li reacts with 2H to form two identical particles.
Identify the particles

Answer; The nuclide 6Li reacts with 2H (also known as deuterium) to form two particles: a 3He nucleus and a 3H nucleus (also known as tritium). The reaction can be represented by the following equation:

6Li + 2H -> 3He + 3H

In this reaction, 6Li is the starting nuclide and 3He and 3H are the products. The 3He nucleus is a helium nucleus with two protons and one neutron, while the 3H nucleus is a hydrogen nucleus with one proton and two neutrons. Both 3He and 3H are stable and are commonly found in nature.

4) Consider a reaction that has a positive ΔH and a positive ΔS. Which of the following statements is TRUE?

A. This reaction will be nonspontaneous at all temperatures.

B. This reaction will be nonspontaneous only at high temperatures.

C. This reaction will be spontaneous only at high temperatures.

D. This reaction will be spontaneous at all temperatures.

E. It is not possible to determine without more information.

5) Consider a reaction that has a positive ΔH and a negative ΔS. Which of the following statements is TRUE?

A. This reaction will be nonspontaneous only at high temperatures.

B. This reaction will be spontaneous at all temperatures.

C. This reaction will be spontaneous only at high temperatures.

D. This reaction will be nonspontaneous at all temperatures.

E. It is not possible to determine without more information.

6) Consider a reaction that has a negative ΔH and a negative ΔS. Which of the following statements is TRUE?

A. This reaction will be nonspontaneous only at high temperatures.

B. This reaction will be spontaneous only at high temperatures.

C. This reaction will be nonspontaneous at all temperatures.

D. This reaction will be spontaneous at all temperatures.

E. It is not possible to determine without more information.

7) For the following example, identify the following.
3O2(g) → 2O3(g)

A. a negative ΔH and a positive ΔS

B. a positive ΔH and a positive ΔS

C. a positive ΔH and a negative ΔS

D. a negative ΔH and a negative ΔS

E. It is not possible to determine without more information.

8) Which statement is true regarding the sublimation of dry ice (solid )?

A. ΔH is positive, ΔS is positive, and ΔG is positive at low temperature and negative at high temperature.

B. ΔH is negative,ΔS is positive, and ΔG is negative at all temperatures.

C. ΔH is negative, ΔS is negative, and ΔG is negative at low temperature and positive at high temperature.

D. ΔH is positive,ΔS is negative, and ΔG is positive at all temperatures.