U q w , is mathematical expression for — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

I need to identify what the mathematical expression **U = q + w** represents in thermodynamics. **Step-by-step reasoning:** 1. **Identify the variables:** - $U$ = Internal energy of a system - $q$ = Heat energy exchanged with surroundings - $w$ = Work done on/by the system 2. **Recognize the fundamental law:** This is the **First Law of Thermodynamics**, which states that the change in internal energy of a system equals the total energy input to the system. 3. **Physical meaning:** - Internal energy ($U$) can change through two mechanisms only: - Heat transfer ($q$): energy transfer due to temperature difference - Work ($w$): energy transfer due to mechanical/non-heat processes 4. **Mathematical expression:** $$\Delta U = q + w$$ Where: - $q > 0$ when heat is absorbed by the system - $w > 0$ when work is done on the system (compression) - $w < 0$ when work is done by the system (expansion) **Answer:** This expression represents the **First Law of Thermodynamics** (or the conservation of energy in thermodynamic form), which establishes that internal energy change depends only on heat and work interactions with the surroundings.