Lecture Notes - Calorimetry and Metal Specific Heat Lab

A: M1V1=M2V2

• Solving for the strontium hydroxide volume.
• Example setup: (50 \times 0.743) / 2 = 1 \times x
• Can also use stoichiometry, paying attention to the 2:1 mole ratio.

B: Finding Final Temperature

• Like previous problems.
• Given: Heat of neutralization of nitric acid (per mole).
• Moles of nitric acid: .743 \times .05
• Multiply moles by heat of neutralization, converting to Joules.
• Use q = mc\Delta{T}, where:
  • q = heat (in Joules)
  • m = total mass (sum of both volumes, assuming 1 gram/mL density)
  • c = specific heat (4.18)
  • \Delta{T} = x - 27.3 (x is the final temperature)

Combustion Problems & Calorimetry

• Problems 13, 15 (example problems) address combustion.

• Problems 14, 16 practice problems.

• Calorimeter: A device with multiple layers to measure heat transfer accurately during a combustion reaction. Key components:

  • Reaction chamber (where combustion occurs). Needs air or oxygen
  • Layer of Water: Surrounds the reaction chamber to absorb the heat of the reaction.
  • Vacuum Layer: Surrounds the water layer to prevent heat transfer to the outside atmosphere.

  Importance:

  • Fructose won't burn underwater.
  • Water coats and prevents oxygen from reaching the combustion material.
  • Water turns to steam when heated which needs to go away.

• Temperature Probe: Measures temperature changes in the water.

• Calorimeters prevent the reaction from being exposed to the air.

Heat Capacity

• Heat capacity includes the mass of the water and the metal components of the calorimeter
• Heat capacity typically measured in kilojoules per degree Celsius.
• q = mc\Delta{T}. The heat capacity is m*c rolled into one variable.
• Vacuum prevents any energy transfer out of the calorimeter.
• Heat\ Capacity \times Change\ in \ Temperature = q

Problem 13

• Fructose (4.5 grams) is burned in a bomb calorimeter containing 1 liter of water.
• Heat capacity of the calorimeter given.
• Temperature rises from 23.49 to 27.72 degrees Celsius.

Q for the Calorimeter

• Two equations needed.
• Q for the mass of water: q = mc\Delta{T}
  q = (1000 \ grams) \times (27.72 - 23.49) \times (4.18 \ J/g^{\circ}C)
  q = 17680.76 \ Joules = 17.68 \ kJ
• Q for the calorimeter (excluding the water):
  Q = C\Delta{T}. Where C = Heat Capacity
  q = 6.97 kJ/^{\circ}C \times (27.72-23.49)^{\circ}C
  q = 29.47 \ kJ

Total Q

• Q total is just summing the above two values: .47 + 17.68 = 47.15 \ kJ
• Since the problem is about 4.5 grams this is the Q released for the 4.5 grams combusted.

Q for One Mole of Fructose

• Use dimensional analysis.
• Molar mass of fructose (C6H{12}O_6) is 180 grams/mole.

Problem 15

• Isooctane combustion in a bomb calorimeter.
• Similar to problem 13, but solving for a different variable.
• Given: 10 mL of isooctane, density 0.688 grams/mL, energy release of 33 kJ/mL.
• Temperature rises from 23.2 to 66.5 degrees Celsius.
• Calorimeter contents: 1 kg of water + calorimeter.

Step 1: Find the Total $q$

• Total energy released: .3 \ kJ/mL \times 10 \ mL = 330 \ kJ

How Much Energy Did the Water Absorb

Water:
q = (1000 \ grams) \times (66.5 - 23.2) \times (4.18) \ J/gC q = (1000 \ grams) \times (43.3) \times (4.18) \ J/gC
q = 181 \ kJ

How Much Did the Calorimeter Absorb

330 \ kJ = q{calorimeter} + 181 \ kJ q{calorimeter} = 149 \ kJ

This allows for solving for the heat capacity of the calorimeter.

Metal Specific Heat Lab

Key Concept

• (Energy\ gained\ by\ water) = (Energy\ lost\ by\ metal)

Why Use Styrofoam Cups?

• Excellent insulators, acting as calorimeters.
• Minimize heat loss, making measurements more accurate.

Why a Large Styrofoam Cup?

• Accommodate metal pieces lying flat.
• Requires less water.

Why Small Amount of Water?

• Water absorbs much energy without temperature change (high specific heat).
• Small water volume maximizes temperature change.
• Reduces the impact of measurement errors, leading to more accurate results.

Procedure

1. Heat metal in hot water (boiling).
2. Measure the temperature of both metal and water
3. Put the metal in the Styrofoam insulated cup
4. Measure the final temperature and compare to initial

Metal Temperature

• Temperature of the hot water in the beaker is the temperature of the metal.

Colligative Properties Reminder

• Impurities in the water like tap water increase as water decreases.
• Solutes goes no where, concentration increases.
• Affects boiling point.