Acids/Bases
DAILY DOUBLE!!
H2SO4 is a(n) ____
NH3 is a(n) ___
H2SO4 is a(n) acid
NH3 is a(n) base
Why do we use the Kelvin scale?
Temperature is in the denominator of gas law equations (ex. Charles' Law, Combined Gas Law), so our temperature scale must be absolute (>0, since we can't divide by zero).
A reaction heats the flask that is holding it. What is the sign of the reaction's delta H and why?
Negative (-) because the reaction is releasing energy (heat), so it is exothermic
Which of the following is a true statement about chemical equilibria in general?
a) Equilibrium is the result of the cessation of all chemical change.
b) There is only one set of equilibrium concentrations that equals the K value.
c) At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction.
d) At equilibrium, the rate constant of the forward reaction is equal to the rate constant for the reverse reaction.
e) At equilibrium, the total concentration of products equals the total concentration of reactants, that is, [products] = [reactants].
Identify the acid and the base in the following reaction:
PO43- + H2O --> HPO42- + OH-
H2O is the acid (loses an H+)
PO43- is the base (gains an H+)
A gas behaves ideally at ______ temperatures and ____ pressure.
High temperatures and low pressure.
The energy required to initiate a chemical reaction
What is activation energy?
Write an expression for the equilibrium constant of the following reaction:
CH4 (g) + 2O2 (g) <--> CO2 (g) + 2H2O (l)
K = [CO2] / [CH4][O2]2
Give the balanced equation for the chemical reaction that occurs between H3PO4 and NH3.
H3PO4 + 3NH3 --> PO43- + 3NH4+
At a constant temperature, a gas starts out with a volume of 516 mL and a pressure of 345 torr. The volume then decreases to 213 mL. What is the new pressure?
P1V1 = P2V2
(345 torr) (516 mL) = (213 mL) P2
P2 = 836 torr
DAILY DOUBLE!!
A measure of a chemical system's potential energy.
(Also describe what the sign of this variable indicates)
What is enthalpy (delta H)?
+ = endothermic (absorbs energy from surroundings)
- = exothermic (releases energy to the surroundings)
Write an equation for the equilibrium constant of the following reaction. At the start of the reaction, is K very large or very small?
N2 (g) + 3H2 (g) <--> 2NH3 (g)
k = [NH3]2 / [N2][H2]3
Very small (large concentration of reactants)
You have 45.6 mL of 10.1 M HBr. You need to use Mg(OH)2 to neutralize it. How many grams of Mg(OH)2 do you need?
1. 2HBr + Mg(OH)2 --> 2H2O + MgBr2
2. 10.1 mol/L * 0.0456 L = 0.461 mol of HBr
3. 0.461 mol HBr * (1 mol Mg(OH)2 / 2 mol HBr) = 0.230 mol of Mg(OH)2
4. 0.230 mol * 58.3 g/mol = 13.4 g of Mg(OH)2
The following reaction is done at STP:
C(s) + 2H2 (g) --> CH4 (g)
If the reaction produces 145 liters of CH4, how many liters of H2 were consumed?
145 L CH4 * (2 L H2 / 1 L CH4) = 290 L of H2
3 sig figs --> 2.90 x 102 L of H2
Determine the sign of delta S for the following reaction and explain your reasoning. What does this sign mean?
HCl (aq) + NaHCO3 (aq) --> H2O (l) + NaCl (aq) + CO2 (g)
The second law of thermodynamics indicates that entropy (delta S) is always increasing (> or = 0). Therefore, this reaction is consistent with this law.
What is true about the K of an equilibrium that strongly favors products?
K >> 1.
You have 137.0 mL of a NaOH solution of unknown concentration and titrate it with a 1.65 M solution of HCl. If it takes 12.47 mL of acid to reach the endpoint, what is the concentration of the NaOH solution?
1. HCl + NaOH --> NaCl + H2O
2. 1.65 mol/L * 0.01247 L = 0.0206 mol HCl
3. 0.206 mol HCl * (1 mol NaOH / 1 mol HCl) = 0.0206 mol NaOH
4. M = 0.0206 mol / 0.137 L = 0.150 M solution of NaOH
In a mixture of two noble gases, the partial pressure of krypton is 771 torr, while the partial pressure of argon is 987 torr. If there are a total of 1.78 moles of gas, how many moles of krypton and argon are present?
PK = 771 / 1,758 = 0.4386
PA = 987 / 1,758 = 0.5614
0.4386 = moles of Kr / 1.78 mol
moles of Kr = 0.781 mol Kr
0.5614 = moles of Ar / 1.78 mol
moles of Ar = 0.999 mol Ar
Determine whether a reaction with a delta H of -255.8 kJ and a delta S of -366.8 J/K is spontaneous at 25.0 degrees C. If not, determine a range of temperatures for which the reaction would be spontaneous.
(delta G = delta H - T*delta S)
delta G = -255,800 J - 298 K (-366.8 J/K)
delta G = -146,000 J --> yes, it is spontaneous at 25.0 *C
For the following reaction at equilibrium, which of the changes below would cause the equilibrium to shift to the left? (choose all applicable answers)
2NOBr (g) <--> 2NO (g) + Br2 (g)
a) Remove some Br2
b) Remove some NOBr
c) Remove some NO
d) Add more NOBr
e) Add more NO
(b) and (e) are correct.