The First Law of Thermodynamics - AP Physics 2
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What is the internal energy change when a system does 100 J of work and absorbs 50 J of heat?
What is the internal energy change when a system does 100 J of work and absorbs 50 J of heat?
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$\triangle U = 50 \text{ J} - 100 \text{ J} = -50 \text{ J}$. Internal energy decreases as more work is done than heat absorbed.
$\triangle U = 50 \text{ J} - 100 \text{ J} = -50 \text{ J}$. Internal energy decreases as more work is done than heat absorbed.
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What does $W$ represent in the First Law of Thermodynamics?
What does $W$ represent in the First Law of Thermodynamics?
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Work done by the system. Energy transferred when system exerts force through displacement.
Work done by the system. Energy transferred when system exerts force through displacement.
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Which sign does $W$ have when work is done by the system?
Which sign does $W$ have when work is done by the system?
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Positive. System expends energy to perform work on surroundings.
Positive. System expends energy to perform work on surroundings.
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Which sign does $W$ have when work is done on the system?
Which sign does $W$ have when work is done on the system?
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Negative. Surroundings perform work on the system, adding energy.
Negative. Surroundings perform work on the system, adding energy.
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Which sign does $W$ have when work is done by the system?
Which sign does $W$ have when work is done by the system?
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Positive. System expends energy to perform work on surroundings.
Positive. System expends energy to perform work on surroundings.
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Identify the process when $Q = W$ and $\triangle U = 0$.
Identify the process when $Q = W$ and $\triangle U = 0$.
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Cyclic process. Process that returns to its initial thermodynamic state.
Cyclic process. Process that returns to its initial thermodynamic state.
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Identify the thermodynamic process with $Q = 0$ and $\triangle U = W$.
Identify the thermodynamic process with $Q = 0$ and $\triangle U = W$.
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Adiabatic process. Process with no heat exchange, so $\triangle U = -W$.
Adiabatic process. Process with no heat exchange, so $\triangle U = -W$.
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Identify the thermodynamic process with $Q = 0$ and $\triangle U = W$.
Identify the thermodynamic process with $Q = 0$ and $\triangle U = W$.
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Adiabatic process. Process with no heat exchange, so $\triangle U = -W$.
Adiabatic process. Process with no heat exchange, so $\triangle U = -W$.
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Find $Q$ if $\triangle U = -10 \text{ J}$ and $W = 5 \text{ J}$.
Find $Q$ if $\triangle U = -10 \text{ J}$ and $W = 5 \text{ J}$.
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$Q = \triangle U + W = -10 \text{ J} + 5 \text{ J} = -5 \text{ J}$. System releases heat since $Q$ is negative.
$Q = \triangle U + W = -10 \text{ J} + 5 \text{ J} = -5 \text{ J}$. System releases heat since $Q$ is negative.
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What is the value of $Q$ if $\triangle U = -10 \text{ J}$ and $W = -10 \text{ J}$?
What is the value of $Q$ if $\triangle U = -10 \text{ J}$ and $W = -10 \text{ J}$?
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$Q = \triangle U + W = -10 \text{ J} - 10 \text{ J} = -20 \text{ J}$. Both terms are negative, indicating energy loss.
$Q = \triangle U + W = -10 \text{ J} - 10 \text{ J} = -20 \text{ J}$. Both terms are negative, indicating energy loss.
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What is the work done if $\triangle U = 0$ and $Q = 100 \text{ J}$?
What is the work done if $\triangle U = 0$ and $Q = 100 \text{ J}$?
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$W = Q = 100 \text{ J}$. In isothermal process, all heat becomes work output.
$W = Q = 100 \text{ J}$. In isothermal process, all heat becomes work output.
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Calculate $\triangle U$ if $Q = 100 \text{ J}$ and $W = 60 \text{ J}$.
Calculate $\triangle U$ if $Q = 100 \text{ J}$ and $W = 60 \text{ J}$.
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$\triangle U = Q - W = 100 \text{ J} - 60 \text{ J} = 40 \text{ J}$. Direct application of the first law formula.
$\triangle U = Q - W = 100 \text{ J} - 60 \text{ J} = 40 \text{ J}$. Direct application of the first law formula.
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Determine the sign of $\triangle U$ if the system releases 30 J of heat and does 10 J of work.
Determine the sign of $\triangle U$ if the system releases 30 J of heat and does 10 J of work.
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Negative. $\triangle U = -30 - 10 = -40$ J, which is negative.
Negative. $\triangle U = -30 - 10 = -40$ J, which is negative.
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What is the First Law of Thermodynamics?
What is the First Law of Thermodynamics?
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Energy cannot be created or destroyed, only transformed. Also known as conservation of energy principle.
Energy cannot be created or destroyed, only transformed. Also known as conservation of energy principle.
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Find the heat added if $\triangle U = 0 \text{ J}$ and $W = 50 \text{ J}$.
Find the heat added if $\triangle U = 0 \text{ J}$ and $W = 50 \text{ J}$.
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$Q = W = 50 \text{ J}$. Isothermal condition where heat input equals work output.
$Q = W = 50 \text{ J}$. Isothermal condition where heat input equals work output.
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Calculate $\triangle U$ if $W = -40 \text{ J}$ and $Q = 60 \text{ J}$.
Calculate $\triangle U$ if $W = -40 \text{ J}$ and $Q = 60 \text{ J}$.
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$\triangle U = Q - W = 60 \text{ J} - (-40 \text{ J}) = 100 \text{ J}$. Negative work means work done on system adds to internal energy.
$\triangle U = Q - W = 60 \text{ J} - (-40 \text{ J}) = 100 \text{ J}$. Negative work means work done on system adds to internal energy.
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What is the work done if $\triangle U = 0$ and $Q = 100 \text{ J}$?
What is the work done if $\triangle U = 0$ and $Q = 100 \text{ J}$?
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$W = Q = 100 \text{ J}$. In isothermal process, all heat becomes work output.
$W = Q = 100 \text{ J}$. In isothermal process, all heat becomes work output.
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What is the relationship between $Q$, $W$, and $\triangle U$ in a cyclic process?
What is the relationship between $Q$, $W$, and $\triangle U$ in a cyclic process?
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$\triangle U = 0$, so $Q = W$. System returns to initial state, so net heat equals net work.
$\triangle U = 0$, so $Q = W$. System returns to initial state, so net heat equals net work.
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Determine $W$ if $Q = 30 \text{ J}$ and $\triangle U = -10 \text{ J}$.
Determine $W$ if $Q = 30 \text{ J}$ and $\triangle U = -10 \text{ J}$.
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$W = Q - \triangle U = 30 \text{ J} + 10 \text{ J} = 40 \text{ J}$. Note: $\triangle U$ is negative, so $W = 30 - (-10) = 40$ J.
$W = Q - \triangle U = 30 \text{ J} + 10 \text{ J} = 40 \text{ J}$. Note: $\triangle U$ is negative, so $W = 30 - (-10) = 40$ J.
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Find the heat added if $\triangle U = 20 \text{ J}$ and $W = 15 \text{ J}$.
Find the heat added if $\triangle U = 20 \text{ J}$ and $W = 15 \text{ J}$.
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$Q = \triangle U + W = 20 \text{ J} + 15 \text{ J} = 35 \text{ J}$. Rearranging the first law to solve for heat input.
$Q = \triangle U + W = 20 \text{ J} + 15 \text{ J} = 35 \text{ J}$. Rearranging the first law to solve for heat input.
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Calculate $\triangle U$ if $Q = -20 \text{ J}$ and $W = 10 \text{ J}$.
Calculate $\triangle U$ if $Q = -20 \text{ J}$ and $W = 10 \text{ J}$.
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$\triangle U = Q - W = -20 \text{ J} - 10 \text{ J} = -30 \text{ J}$. System loses heat and has work done on it.
$\triangle U = Q - W = -20 \text{ J} - 10 \text{ J} = -30 \text{ J}$. System loses heat and has work done on it.
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What is the internal energy change for a system doing 15 J of work and absorbing 15 J of heat?
What is the internal energy change for a system doing 15 J of work and absorbing 15 J of heat?
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$\triangle U = Q - W = 15 \text{ J} - 15 \text{ J} = 0 \text{ J}$. Equal heat input and work output results in no change.
$\triangle U = Q - W = 15 \text{ J} - 15 \text{ J} = 0 \text{ J}$. Equal heat input and work output results in no change.
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What is the change in internal energy for an isolated system?
What is the change in internal energy for an isolated system?
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$\triangle U = 0$. No energy exchange with surroundings means no change.
$\triangle U = 0$. No energy exchange with surroundings means no change.
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What is $\triangle U$ if $Q = 25 \text{ J}$ and $W = -25 \text{ J}$?
What is $\triangle U$ if $Q = 25 \text{ J}$ and $W = -25 \text{ J}$?
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$\triangle U = Q - W = 25 \text{ J} - (-25 \text{ J}) = 50 \text{ J}$. Work done on system plus heat input both increase energy.
$\triangle U = Q - W = 25 \text{ J} - (-25 \text{ J}) = 50 \text{ J}$. Work done on system plus heat input both increase energy.
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Find the internal energy change if $Q = 0$ and $W = -25 \text{ J}$.
Find the internal energy change if $Q = 0$ and $W = -25 \text{ J}$.
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$\triangle U = -W = 25 \text{ J}$. Negative work means work is done on the system.
$\triangle U = -W = 25 \text{ J}$. Negative work means work is done on the system.
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Identify the process when $Q = W$ and $\triangle U = 0$.
Identify the process when $Q = W$ and $\triangle U = 0$.
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Cyclic process. Process that returns to its initial thermodynamic state.
Cyclic process. Process that returns to its initial thermodynamic state.
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What does $Q$ represent in the First Law of Thermodynamics?
What does $Q$ represent in the First Law of Thermodynamics?
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Heat added to the system. Energy transferred into or out of the system.
Heat added to the system. Energy transferred into or out of the system.
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What is the value of $Q$ if $\triangle U = -10 \text{ J}$ and $W = -10 \text{ J}$?
What is the value of $Q$ if $\triangle U = -10 \text{ J}$ and $W = -10 \text{ J}$?
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$Q = \triangle U + W = -10 \text{ J} - 10 \text{ J} = -20 \text{ J}$. Both terms are negative, indicating energy loss.
$Q = \triangle U + W = -10 \text{ J} - 10 \text{ J} = -20 \text{ J}$. Both terms are negative, indicating energy loss.
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Find $Q$ if $\triangle U = -10 \text{ J}$ and $W = 5 \text{ J}$.
Find $Q$ if $\triangle U = -10 \text{ J}$ and $W = 5 \text{ J}$.
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$Q = \triangle U + W = -10 \text{ J} + 5 \text{ J} = -5 \text{ J}$. System releases heat since $Q$ is negative.
$Q = \triangle U + W = -10 \text{ J} + 5 \text{ J} = -5 \text{ J}$. System releases heat since $Q$ is negative.
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Which sign does $Q$ have when heat is released by the system?
Which sign does $Q$ have when heat is released by the system?
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Negative. Heat flows out of the system, decreasing its energy.
Negative. Heat flows out of the system, decreasing its energy.
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