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The groundwater sample was analysed. The measured pH of the test water at 25°C had a value, pH = 3.8. The concentration of Zn^2+ ions in water was also determined to be 4.132·10^-2 mol/L.
Groundwater is in equilibrium with sediment containing MnO2 and ammonia. Calculate the
concentration of NH4^+ ions under these conditions.
Standard reduction electrode potentials for reactions:
Zn ^2+ + 2e →Zn E°= -0.76V
2MnO 2 + 2NH4^+ +2e → Mn2O3 +2NH3
+ H2O
E°= 0.74 V
Write a sum cell reaction.
The groundwater sample was analysed. The measured pH of the test water at 25°C had a value, pH = 3.8. The concentration of Zn2+ ions in water was also determined to be 4.132·10-2 mol/L.
Groundwater is in equilibrium with sediment containing MnO2 and ammonia. Calculate the
concentration of NH4+ ions under these conditions.
Standard reduction electrode potentials for reactions:
Zn 2++ 2e →Zn E°= -0.76V
2MnO 2 + 2NH4+ 2e → Mn2O3 +2NH3+ H2O
E°= 0.74 V
Write a sum cell reaction.
Calculate the mass of sodium chloride that must be added per kilogram of ice so that it melts at -5°C . The degree of salt dissociation in this solution is 90%
Calculate the ^H for the dissolution reaction of salts below using the thermodynamic data given
a)LiCl -408.61kj/mol
b)NaBr -360.0 kJ/mol
Calculate the change the entropy, Change in Gibbs free energy, change in Enthalpy and change in Volume if 0.5mol of Oxygen is mixed with 0.5mol of Nitrogen at 25 degree Celsius and 1 atm assuming they are Ideal gases.
Consider a flat sheet of iron at 300 K does not receive any radiation from its surroundings. The metal is 10 cm x 10 cm x 0.1 cm; the heat capacity is 25 J/K mol; the density is 7.86 g/cm3
a) How many joules per second are lost by radiation initially? Assume that one flat side only radiates into space.
Answer: 4.59 Watts
b) After 20 minutes, what is the temperature of the metal plate?
Answer: 219Kelvin
SHOW SOLUTION!
The lattice energy for KCl is -715 kJ/mol and this is the energy given off (a negative number) when this lattice forms. We are interested in the opposite process, when the lattice is disrupted. Using the lattice energy value (absolute value), calculate the energy required to separate the ions in 25.00g of KCl (MW = Molar mass 74.555 g/mol). Report your answer with 1 decimal place.
5a) What is change in the internal energy E for an ideal gas if its volume changes at constant temperature?
5b) What can you say about the change in the internal energy E for a real gas in which the gas molecules repel each other as its volume changes at constant temperature?
5c) For the gases in parts a and b, what can you say about the change in their internal energy E when the temperature is changed at constant volume?
How much heat energy is required to convert 200.0 g of ice at −20 oC to all steam at 110 oC at 1 atm?
How can you assume that Sij = 0 for all i and j. For example S12, how can the overlap integral of two adjacent Pz orbitals (one on the carbon and one on the adjacent oxygen) equal zero? Similarly for the other overlap integrals S13=S14=S21=S31=S41 .
