GASES 

Know: 1L = 1000ml = 1000cm³ = 1 dm³
Know: 760mmHg = 1.00atm = 101.3kPa = 14.7psi
For Free: 1Pa = 1 Newton/m² = F/A

Look!  Laws... like the Law of the Burrito: "If a person ever eats a burrito with beans and hot sauce within five seconds, then he will produce enormous quantities of methane gas from the opposite end of his digestive system."

So V a nT_k /P (what does that a?  it reads, "V is proportional to nT/P")
V = RnT_k /P or PV = nRT_k

--

See p. 101 for R values
Know eq.’s 4.12 & 4.13 p.104

--

Find density of O₂ at 27⁰C, 735 mmHg:

        PV = nRT or PV = g/mm * RT
           Also d = g/V = P(MM)/RT
                                          = (735/760atm)(32.0g/mol)
                                                (0.0821L*atm/mol K)(300K)
                                          = 1.26 g/L

What mass of Zn is needed to react with hydrochloric acid to form 16.0L of H₂(g) @ 20⁰C, 735mmHg?

                Zn(s) + 2 HCl(aq) --> ZnCl₂(aq) + H₂(g)
                       Zn(s) + 2H⁺ (aq) --> Zn⁺²(aq) + H₂(g)

                    V = 16.0L
                             T = 20⁰C
                             P = 735mmHg

                 n = PV = (735/760atm)(16.0L) = 0.643 mol H₂
                                  RT  (0.0821Latm/molK)(293K)

                 0.643 mol H₂ x 1mol Zn x 65.38g Zn = 42.0g Zn
                                                              1 mol H₂       1mol Zn

                H₂(g) + Cl₂(g) --> 2HCl (g)

Coeff can stand for 1.____ 2. ____ 3.____.

p.108 and t-shirt
At STP, 22.4L/mol for ideal gas.

--

Dalton’s Law of Partial Pressure See p. 109

P_T = S P_i = P₁ + P₂ +…+P_n
i=1
p. 111
P₁ = X₁P_T where X₁ = n₁/n_total [mole fraction]

So P_t is?

How do you find P_H2O? Appendix A1

Suppose we collect 256ml of gas at 22⁰C, and a pressure of 752 mmHg. Find pressure of H₂, moles H₂, mole fraction H₂.

P_t = P_H2+ P_H2O --> P_H2 = P_t – P_H20
P_H2 = 752 – 20 = 732mmHg
n=PV/RT= (732/760)(0.256)/(0.0821)/(295) = 0.0102 mol
X_H2 = P_H2/P_t = 732/752 = 0.973

Know p. 112

The postulates of the kinetic molecular theory can be stated as follows:

Gases consist of particles, which have the following properties:

• The particles are so small compared to the distances between them that the volume of the individual particles can be assumed to be negligible (zero).
• The particles are in constant motion. The collisions of the particles with the walls of the container are the cause of the pressure exerted by the gas.
• The particles are assumed to exert no forces of each other; they are assumed neither to attract nor to repel each other.
• The average kinetic energy of a collection of gas particles is assumed to be directly proportional to the Kelvin temperature of the gas.

KE_T = ½ mv² =cT_k
m = mass, v = speed, c = constant

See p.113

Diffusion vs. Effusion

(Rate Eff. A)/(Rate Eff. B)
= (Ave v_a)/(Ave v_b)
= [(MM_b)/(MM_a)]^½
= (time B)/(time A)

Ave v = (3RT/MM)^½

For H₂ at 0⁰C,
Ave v = [3*8.31(kg*m² /mol*K*s²)273K]/[0.002016kg/mol]
          = 1.84 x 10³m/s

Know why gases deviate from ideal gases. See p. 119.

    Low temperature, attractive force important.
    High pressure, finite volume important.

Back to the Class Notes Homepage
 

Maintained by: Chris Weilemann Lee Marek