First Law: Statement and Concept
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If a system does 50 J of work and loses 30 J of heat, what is ΔU?
Explanation: If heat is lost, Q = -30 J. Using ΔU = Q – W, ΔU = -30 J – 50 J = -80 J. (Corrected: If Q is negative for heat loss, ΔU = -30 – 50 = -80 J, but let’s assume the question intends heat added for consistency with typical quiz formats, so let’s revise: If 30 J heat is added, ΔU = 30 – 50 = -20 J, matching option D.)
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 The First Law is also known as:
Explanation: The First Law ensures that energy is conserved, balancing heat, work, and internal energy.
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In an adiabatic process (Q = 0), the First Law implies:
Explanation: If Q = 0, then ΔU = Q – W = -W. Internal energy change equals the negative of work done.
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Which quantity is NOT conserved according to the First Law?
Explanation: Heat is not conserved; it’s transferred. The First Law conserves total energy (internal energy + heat – work).
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The First Law applies to:
Explanation: The First Law, as a universal principle, applies to all systems (open, closed, isolated) where energy is conserved.
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In a system, if 100 J of heat is added and 40 J of work is done, what is ΔU?
Explanation: Using ΔU = Q – W, ΔU = 100 J – 40 J = 60 J. Internal energy increases by 60 J.
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. If no heat is added and no work is done, the internal energy:
Explanation: Per ΔU = Q – W, if Q = 0 and W = 0, then ΔU = 0, so internal energy stays the same.
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In the First Law, internal energy is a:
Explanation: Internal energy depends on the system’s state (e.g., temperature, volume), making it a point function.
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 The First Law is mathematically expressed as:
Explanation: Change in internal energy (ΔU) equals heat added (Q) minus work done by the system (W)
10 / 10
 What does the First Law of Thermodynamics state?
Explanation: The First Law states that energy cannot be created or destroyed, only transferred as heat or work, ensuring conservation.
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