# Mid Term Chem

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MgCl2(aq) + 2NaOH(aq) → 2NaCl(aq) + Mg(OH)2(s)

A 100mL sample of 0.1M MgCl2(aq) and a 100mL sample of 0.2M NaOH(aq) were combined, and Mg(OH)2(s) precipitated, as shown by the equation above. If the experiment is repeated using solutions of the same molarity, which of the following changes in volume will double the amount of Mg(OH)2(s) produced?
A. Using the same volume of MgCl2(aq)MgCl2(aq) but twice the volume of NaOH(aq)
B.Using twice the volume of MgCl2(aq)MgCl2(aq) but half the volume of NaOH(aq)
C.Using twice the volume of MgCl2(aq)MgCl2(aq) but the same volume of NaOH(aq)
D. Using twice the volume of MgCl2(aq)MgCl2(aq) and twice the volume of NaOH(aq)
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

A student had two dilute, colorless solutions, HCl(aq) and NaOH(aq), which were at the same temperature. The student combined the solutions, and the reaction represented above occurred. Which of the following results would be evidence that a chemical reaction took place?
A. The resulting solution is colorless.
B. The temperature of the reaction mixture increases.
C. The total volume of the mixture is approximately equal to the sum of the initial volumes.
D. The resulting solution conducts electricity.
The graphs above show Maxwell-Boltzmann distributions for one-mole samples of Ar(g). Graph 1 shows the distribution of particle energies at 300K and graph 2 shows the distribution of particle energies at 600K. A student predicts that if the samples are combined in an insulated container and thermal equilibrium is attained, then the most probable particle energy will be between the most probable energy shown in graph 1 and the most probable energy shown in graph 2. Which of the following is the best justification for the student's claim?
A. When the samples are combined, the gas particles will collide with one another, with the net effect being that the speed of the lowest energy particles decreases while the speed of the highest energy particles increases, leaving the average speed of the particles in the original samples unchanged.
B. When the samples are combined, the gas particles from each sample will collide with the gas particles from the other sample until every particle in the mixture has the same speed, which is between the average speed of the particles in the hotter sample and the average speed of the particles in the cooler sample.
C.When the samples are combined, the gas particles collide with one another until every particle in the mixture has the same kinetic energy, which is between the average kinetic energy of the particles in the hotter sample and the average kinetic energy of the particles in the cooler sample.
D. When the samples are combined, the gas particles will collide with one another, with the net effect being that energy will be transferred from the more energetic particles to the less energetic particles until a new distribution of energies is achieved at a temperature between 300K and 600K.
A 1L sample of helium gas at 25°C and 1atm is combined with a 1L sample of neon gas at 25°C and 1atm. The temperature is kept constant. Which of the following statements about combining the gases is correct?
A. The average speed of the helium atoms increases when the gases are combined.
B. The average speed of the neon atoms increases when the gases are combined.
C. The average kinetic energy of the helium atoms increases when the gases are combined.
D. The average kinetic energy of the helium atoms and neon atoms do not change when the gases are combined.
A student uses visible spectrophotometry to determine the concentration of CoCl2(aq) in a sample solution. First the student prepares a set of CoCl2(aq) solutions of known concentration. Then the student uses a spectrophotometer to determine the absorbance of each of the standard solutions at a wavelength of 510nm and constructs a standard curve. Finally, the student determines the absorbance of the sample of unknown concentration.
A wavelength of 510nm corresponds to an approximate frequency of 6×1014s−1. What is the approximate energy of one photon of this light?
A. 9 × 10^47 J
B. 3 x 10^17 J
C. 5 x 10^-7 J
D. 4 x 10^-19 J