Question

1. A woman expends 92 kJ of energy in walking a kilometer. The energy is supplied by the metabolic breakdown of food intake and has a 35 percent efficiency. a) If the woman drives a car over the same distance, how much energy is used if the car gets 8.0 km per liter of gasoline (approximately 20 mi/gal)? The density of gasoline is 0.71 g/mL, and its enthalpy of combustion is 49 kJ/g. b) Compare the efficiencies of the two processes.

2. In a constant-pressure calorimetry experiment, a reaction gives off 23.8 kJ of heat. The calorimeter contains 150 g of water, initially at 25.4°C. What is the final temperature of the water? The heat capacity of the calorimeter is negligibly small.

3. A 48.0−g sample of an unknown metal at 99° C was placed in a constant-pressure calorimeter containing 75.0 g of water at 24.0°C. The final temperature of the system was found to be 28.4°C. Calculate the specific heat of the metal. (The heat capacity of the calorimeter is 14.4 J/4.

4.  A piece of silver with a mass 4.10 ×10² g has a heat capacity of 97.2 J/°. C. What is the specific heat of silver?°

5. Protons can be accelerated to speeds near that of light in particle accelerators. Estimate the wavelength (in nm) of such a proton moving at 2.91 × 10⁸ m/s (mass of a proton = 1.673 × 10⁻²⁷ kg).  Enter your answer in scientific notation.

6. The ionization energy of a certain element is 452 kJ/mol. (Ionization energy is the minimum energy required to remove an electron from an atom. It is usually expressed in units of kJ/mol; that is, it is the energy in kilojoules required to remove one mole of electrons from one mole of atoms.) However, when the atoms of this element are in the first excited state, the ionization energy is only 126 kJ/mol.

Based on this information, calculate the wavelength of light emitted in a transition from the first excited state to the ground state.

Answer 1