Salad Quiz 5

A solution calorimeter was inadvertently calibrated with 105 mL of water instead of 100 mL. The calorimeter was emptied and dried and then used to determine the heat of reaction of powdered zinc in 100 mL of HCl (aq). It can be deduced from this information that the correct calibration factor should be

• Lower and the heat of reaction should be lower.
• Higher and the heat of reaction should be higher.
• Lower and the heat of reaction should be higher.
• Higher and the heat of reaction should be lower.

A solution calorimeter is used in two experiments to examine the endothermic reaction of ammonium nitrate with water. In the first experiment 10.0 g of NH₄NO₃ was added to 100.0 mL of water at 25°C in the calorimeter. In the second experiment 100.0 g of NH₄NO₃ was added to 100.0 mL of water at 25°C. The temperature of the second experiment compared with the first will

• Fall at the same rate to the same temperature
• Fall at the same rate to a lower temperature
• Fall at the faster rate to the same temperature
• Fall at the faster rate to a lower temperature

The reaction between solutions of hydrochloric acid and sodium hydroxide can be represented by the following equation.
HCl(aq)+NaOH(aq)→NaCl(aq)+H₂O(l); ΔH=-56 kJ mol^-1
60.0ml of 2.0M HCl, at 21^oC, is mixed with 40.0mL of 2.0M NaOH, also at 21^oC, in a well-insulated calorimeter. The calibration factor for the calorimeter and contents is 420 J K^-1. The final temperature, in ^oC, of the resultant solution in the calorimeter would be closest to

• 11
• 32
• 37
• 52

Humans obtain all of their energy requirements from the food they eat. The amount of energy in food can be measured using a bomb calorimeter. The following are steps, in random order, that are taken to determine experimentally the energy content of a sample of a food, using a bomb calorimeter.
1. Measure the rise in temperature.
2. Fill the calorimeter with water and wait until the temperature has reached a steady value.
3. Accurately weigh the sample of the food and place it inside the sealed compartment or 'bomb' in the presence of excess oxygen.
4. Measure the rise in temperature again.
5. Pass a measured amount of electrical energy into the system.
6. Ignite the sample with electrical ignition wires. 
Which one of the following alternatives best presents an appropriate sequence of procedures?

• 5, 1, 3, 2, 4, 6
• 2, 3, 1, 5, 6, 4
• 3, 2, 5, 1, 6, 4
• 3, 6, 1, 2, 5, 4

Tags

NGSS.HS-PS3-4

A chemist used bomb calorimetry to measure the enthalpy change (ΔH) for the combustion of butane. 
The calibration factor (CF) of the calorimeter was determined by measuring the temperature rise (ΔT₁) that occurred when a known amount of charge (Q) was passed through the heating element in the calorimeter at a measured voltage (V). The CF, in J^oC^-1, is

• Q/(VxΔT₁)
• ΔT₁/(QxV)
• VxQxΔT₁
• (VxQ)/ΔT₁

For the reaction KOH(s) →KOH(aq); ΔH=-55.6 kJ mol^-1, the temperature of water in the calorimeter is measured and then 1.00 g KOH is dissolved in the water. In order to return the calorimeter to the temperature it was prior to the addition of the KOH.

• 991 J of energy must be supplied from outside the calorimeter
• 991 kJ of energy must be removed from the calorimeter
• 55.6 kJ of energy must be supplied from outside the calorimeter
• 55.6 kJ of energy must be removed from the calorimeter

An energy profile for a reversible chemical reaction is shown. According to this profile, the activation energy of the reverse reaction is equal to

• D
• C - B
• A - B
• C- D

Tags

NGSS.HS-PS1-4

When 50 g of water at 90^oC is added to a calorimeter containing 50 g of water at 15^oC, the temperature increases to 45^oC. Assuming no energy is lost to the environment, the energy absorbed by the calorimeter is equal to the

• energy lost by the hot water
• energy gained by the cold water
• sum of the energy gained by the cold water and the energy lost by the hot water
• difference between the energy lost by the hot water and the energ gained by the cold water

Which of the following statement regarding the energy changes for a particular exothermic chemical reaction is NOT correct?

• The activation energy of the forward reaction is lower than the activation energy of the reverse reaction.
• The enthalpy value of the products is lower than the enthalpy value of the reactants.
• The value of the activation energy of the reverse reaction is lower than the change in enthalpy value.
• The forward and reverse reactions both require the absorption of some energy.