Improve Device Design Practice Test

Students tested two possible modifications to improve a hot pack that currently stays above $40^\circ\text{C}$ for only 1 hour (criterion: 2+ hours). The peak temperature is already acceptable at $46^\circ\text{C}$.

Option 1: Add 20 g more calcium chloride (no change to insulation).

Option 2: Keep the same chemicals but add a thicker insulating wrap.

Which option most directly targets the likely root cause of the hot pack failing the 2-hour criterion?

A hot pack prototype uses 40 g of calcium chloride in a zip bag, wrapped in one layer of felt. Criterion: stay at or above $40^\circ\text{C}$ for 2 hours.

Test results (temperature vs. time):

• 5 min: $45^\circ\text{C}$
• 30 min: $42^\circ\text{C}$
• 60 min: $39^\circ\text{C}$
• 120 min: $30^\circ\text{C}$

Which statement best explains why a design modification is needed?