Investigating Variables Affecting Temperature Changes in Chemical Reactions

Objective

• Understand how to investigate variables that affect temperature changes in chemical reactions.
• Focus on an exothermic reaction: neutralization of hydrochloric acid (HCl) and sodium hydroxide (NaOH).

Key Concepts

• Exothermic vs. Endothermic Reactions: Exothermic reactions release energy, increasing temperature.
• Independent Variable: Volume of NaOH solution.
• Dependent Variable: Maximum temperature reached.
• Control Variables: Volume and concentration of HCl and NaOH.

Experimental Procedure

1. Setup:
   • Measure 30 cm³ of dilute HCl using a measuring cylinder.
   • Pour HCl into a polystyrene cup placed inside a beaker (prevent spills).
   • Measure the initial temperature of the acid with a thermometer.
2. Reaction Process:
   • Measure 5 cm³ of NaOH solution and add to the HCl in the cup.
   • Cover the cup with a lid, insert a thermometer through the lid into the solution.
   • Stir gently, observe the temperature change.
   • Record the highest temperature reached.
3. Repetition:
   • Repeat the experiment, increasing NaOH volume by 5 cm³ each time, up to 40 cm³.
   • Perform the entire experiment twice for accuracy.
4. Data Analysis:
   • Calculate the mean maximum temperature for each NaOH volume.
   • Plot a graph showing the relationship between NaOH volume and maximum temperature.

Observations

• As NaOH volume increases, the maximum temperature increases.
• Beyond a certain volume, the temperature begins to decrease due to limited HCl.
• Excess NaOH results in some unreacted solution, spreading out the energy and lowering the maximum temperature.

Explanation

• Graph Interpretation: More NaOH means more particles to react, releasing more energy until HCl becomes insufficient.
• Temperature Decrease: Due to increased solution volume, energy is spread, reducing temperature rise.

Practical Considerations

• Using a Polystyrene Cup and Lid:
  • Reduces heat loss, ensuring accurate temperature measurement.
  • Polystyrene insulates sides/bottom; the lid minimizes air exposure losses.

Study Resources

• Refer to the vision workbook for additional practice questions related to this experiment.