Chemical Concepts 222

What is the empirical formula of a compound of carbon, hydrogen, and oxygen that contains 51.56% carbon and 14.09% hydrogen by mass?

To find the empirical formula, convert the percentages to moles by dividing by the atomic masses of C (12.01 g/mol), H (1.008 g/mol), and O (16.00 g/mol). The empirical formula is determined by finding the simplest whole-number ratio of moles.

How many moles of the excess reagent remain when 0.30 mol NH3 reacts with 0.40 mol O2 to produce NO and H2O?

Using the balanced equation 4NH3 + 5O2 → 4NO + 6H2O, calculate the limiting reagent and then determine the moles of the excess reagent remaining after the reaction.

What is the theoretical yield of lead that can be obtained by the complete reaction of 57.33 g PbO?

Using the reaction 2PbO + PbS → 3Pb + SO2, calculate the moles of Pb produced from 57.33 g of PbO and convert to grams to find the theoretical yield. The percent yield is calculated by (actual yield/theoretical yield) x 100.

Arrange CsBr, NaCl, and RbBr in increasing magnitude of lattice energy.

The correct order is CsBr < RbBr < NaCl, as lattice energy increases with charge and decreases with ionic size.

What gas exerts a pressure of 1.13 atm in a 10.0 L vessel at 100.0 °C with a mass of 10.0 grams?

Calculate the molar mass using the ideal gas law (PV=nRT) to determine which gas matches the calculated molar mass.

What is the partial pressure of oxygen in a mixture of 3.25 moles of O2 and 2.75 moles of N2 exerting a total pressure of 22.4 atm?

Use Dalton's Law of Partial Pressures: P(O2) = (moles of O2/total moles) x total pressure.

For a gas sample containing equimolar amounts of nitrogen and hydrogen at 300 K, how do their average speeds and kinetic energies compare?

Hydrogen has a higher average speed and the same average kinetic energy compared to nitrogen due to its lower molar mass.

Which of the following has hydrogen bonding intermolecular forces?

HF exhibits hydrogen bonding due to the presence of highly electronegative fluorine bonded to hydrogen.

Which pure substance has the lowest vapor pressure at 25 °C?

H2O has the lowest vapor pressure due to strong hydrogen bonding.

Which compound is expected to be the most soluble in ethanol (CH3CH2OH)?

NH3 is expected to be the most soluble in ethanol due to hydrogen bonding.

What is the molal concentration of a 3.539 M HNO3 aqueous solution with a density of 1.150 g/ml?

Calculate molality using the formula: molality = moles of solute/kg of solvent.

What is the freezing point of a solution with 2.50 g of naphthalene (C10H8) dissolved in 100 g of benzene?

Use the freezing point depression formula: ΔTf = Kf * m, where Kf for benzene is 5.07 °C/m.

Which aqueous solution will have the lowest boiling point?

0.04 M MgCl2 will have the lowest boiling point due to the highest van 't Hoff factor, resulting in more particles in solution.

What mass of Cl2(g) is needed to release 45.2 kJ of energy during the reaction of carbon and chlorine gas?

Use the reaction enthalpy ΔH = -135.4 kJ/mol to calculate the mass of Cl2 needed.

What is the mass of iron after heating and placing it in water at equilibrium?

Use the heat transfer equation q = mcΔT to find the mass of iron.

How to calculate the standard enthalpy change for a reaction using standard enthalpies of formation?

ΔH° = ΣΔHf°(products) - ΣΔHf°(reactants).

What is the rate law for the reaction 2H2(g) + Cl2(g) → 2HCl(g)?

Determine the rate law based on initial rate data and the change in concentration of reactants.

What mass remains of a 200.0 g sample of a radioactive isotope after 60 years with a half-life of 10.0 years?

Use the formula: remaining mass = initial mass * (1/2)^(time/half-life).

What will the concentration of NOCl be after 45 minutes if it is second order?

Use the second-order integrated rate law: 1/[A] = kt + 1/[A0].

How to determine the activation energy from rate constants at different temperatures?

Use the Arrhenius equation and the slope of the plot of ln(k) versus 1/T.

How can activation energy be experimentally determined?

Activation energy can be determined from the slope of the plot of ln(k) versus 1/T.