Chemistry Thermochemistry BUMHS 2024
PMDC Verified Question 18 of 81
The sign of heat "q" is positive for a system when:
A
Heat flows from surrounding to system
B
The temperature of system drops
C
Heat flows from system to surrounding
D
No flow of heat between system to surrounding
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: Heat flows from surrounding to system
Concept:

Thermodynamic sign conventions are established entirely from the perspective of the chemical system.

Formula:

$$ +q = \text{System absorbs energy} $$
$$ -q = \text{System loses energy} $$

Solution:

  • If a system's internal energy increases because of a thermal transfer, we mathematically denote that addition with a positive sign.


  • This strictly occurs when heat flows from the surroundings into the system (an endothermic process).


Why other options are incorrect:

When heat flows from system to surroundings (exothermic), the system loses energy, making \( q \) negative. No flow of heat implies \( q = 0 \) (adiabatic).

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