First Law of Thermodynamics, Basic Introduction, Physics Problems

The Organic Chemistry Tutor
1 Dec 201710:30
EducationalLearning
32 Likes 10 Comments

TLDRThe video script discusses the first law of thermodynamics, focusing on how the internal energy of a system changes with heat transfer and work done. It explains the sign conventions for heat (q) and work (w) in physics and chemistry, and provides examples to illustrate the calculation of internal energy changes. The script covers scenarios where heat is added or removed, and work is performed by or on a system, emphasizing the conservation of energy principle.

Takeaways
  • 📚 The first law of thermodynamics is based on the principle of conservation of energy, stating that energy cannot be created or destroyed, only transferred or changed in form.
  • 🔄 Changes in a system's internal energy can occur through heat transfer (Q) or work done by/on the system (W).
  • 🌡️ Positive Q indicates heat energy is added to the system, while negative Q indicates heat energy is removed.
  • ⚙️ Positive W indicates work is done by the system, and negative W indicates work is done on the system.
  • 🔢 The formula for calculating the change in internal energy (ΔU) of a system is ΔU = Q - W.
  • 📈 In the first problem, the system's internal energy increased by 100 joules due to the addition of 300 joules of heat energy and the performance of 200 joules of work.
  • 📉 In the second problem, the system's internal energy decreased by 300 joules when 700 joules of heat energy were removed and 400 joules of work were done on the system.
  • 🔩 The work done by a gas at constant pressure can be calculated using the formula: Work = P * ΔV, where P is pressure in pascals and ΔV is the change in volume in cubic meters.
  • 💥 1350 joules of work were performed by the gas in the third problem when it expanded at a constant pressure of 45,000 pascals from 0.02 to 0.05 cubic meters.
  • 📉 In the fourth problem, the internal energy of the gas increased by 150 joules when 1500 joules of heat energy were added and 1350 joules of work were done on the gas.
  • 📈 Finally, the internal energy of the gas in the last problem increased by 539 joules when 2500 joules of heat energy were removed and 3039 joules of work were done on the gas during compression.
Q & A

  • What is the formula used to calculate the change in internal energy of a system?

    -The formula used is ΔU = q - w, where ΔU represents the change in internal energy, q is the heat energy added to or removed from the system, and w is the work done by or on the system.

  • What is the First Law of Thermodynamics?

    -The First Law of Thermodynamics, also known as the principle of conservation of energy, states that energy cannot be created or destroyed, only transferred or changed from one form to another.

  • How does the sign convention for q and w work in physics?

    -In physics, if q is positive, it means heat energy is added to the system, and if it is negative, heat energy is removed. Similarly, if w is positive, it means work is done by the system, and if it is negative, work is done on the system.

  • How does the sign convention for work differ between physics and chemistry?

    -In chemistry, a positive sign for work indicates work is done by the system, which is the opposite of physics where a positive sign indicates work is done on the system.

  • What are the two ways to change the internal energy of a system in thermodynamics?

    -The two ways to change the internal energy of a system are by transferring heat energy to or from it or by performing mechanical work on the system or by the system itself.

  • In the first problem, how much work was performed by the system and what was the resulting change in internal energy?

    -The system performed 200 joules of work (w = +200 J), and the resulting change in internal energy was an increase of 100 joules (ΔU = +100 J), calculated as 300 J (heat added) - 200 J (work done).

  • In the second problem, what was the net change in internal energy when 700 joules of heat energy was removed and 400 joules of work was done on the system?

    -The net change in internal energy was a decrease of 300 joules (ΔU = -300 J), calculated as -700 J (heat removed) + 400 J (work done on the system).

  • How can work performed by a gas at constant pressure be calculated?

    -Work performed by a gas at constant pressure can be calculated using the formula W = P × ΔV, where W is the work, P is the constant pressure, and ΔV is the change in volume.

  • What was the work performed by the gas and the change in internal energy in the third problem?

    -The gas performed 1350 joules of work (W = +1350 J), and the change in internal energy was an increase of 150 joules (ΔU = +150 J), calculated as 1500 J (heat added) - 1350 J (work performed by the gas).

  • How was the work calculated for the compressed gas in the fourth problem?

    -The work done on the compressed gas was calculated as -30 L × atm × 101.3 J/(L × atm), which equals -3039 J. The negative sign indicates that work was done on the gas, not by it.

  • What was the final change in internal energy when 2500 joules of heat energy was removed from the gas and work was done on it in the fourth problem?

    -The final change in internal energy was an increase of 539 joules (ΔU = +539 J), calculated as -2500 J (heat removed) - (-3039 J) (work done on the gas).

Outlines
00:00
🔧 First Law of Thermodynamics and Energy Change Calculation

This paragraph introduces the concept of the First Law of Thermodynamics, which is the principle of conservation of energy. It explains how the internal energy of a system can be changed by either doing work on the system or by heat transfer. The paragraph provides a formula for calculating the change in internal energy (ΔU) as the difference between heat energy added (Q) and work performed by the system (W). Two examples are worked out: one where 300 joules of heat are added and 200 joules of work are performed by the system, resulting in a 100 joule increase in internal energy, and another where 700 joules of heat are removed and 400 joules of work are done on the system, resulting in a 300 joule decrease in internal energy.

05:00
📈 Work Calculation at Constant Pressure and Energy Change

This paragraph focuses on calculating the work performed by or on a gas at constant pressure and the subsequent change in internal energy. It explains the formula for work done at constant pressure (Work = P × ΔV) and uses it to calculate the work done by a gas that expands from 0.02 to 0.05 cubic meters against a pressure of 45,000 pascals, which is 1350 joules. The paragraph also covers a scenario where 1500 joules of heat energy are added to the gas, resulting in a 150 joule increase in internal energy. Another example involves 2500 joules of heat energy being removed from a gas compressed from 25 to 15 liters at a pressure of 3 atm, resulting in a 539 joule increase in internal energy.

10:05
📝 Summary and Conclusion

This paragraph serves as a brief conclusion to the video script, summarizing the key points discussed. It reiterates the importance of understanding the First Law of Thermodynamics and the methods by which the internal energy of a system can be altered. The paragraph emphasizes the practical application of the formulas for calculating work done and energy changes in thermodynamic systems, highlighting the significance of these concepts in both physics and chemistry.

Mindmap
Keywords
💡Internal Energy
Internal energy is the total energy contained within a system, which includes kinetic and potential energy of the molecules. It is a key concept in thermodynamics and is related to the system's temperature and phase. In the video, the change in internal energy (ΔU) is calculated using the formula ΔU = q - w, where q represents heat energy added or removed, and w represents work done by or on the system.
💡First Law of Thermodynamics
The First Law of Thermodynamics, also known as the Law of Energy Conservation, states that energy cannot be created or destroyed, only transferred or changed in form. It is fundamental to understanding how heat and work interact within a closed system. In the context of the video, this law is used to explain how the internal energy of a system changes when heat is added or removed, and when work is done.
💡Heat Energy (q)
Heat energy (q) is the thermal energy transferred between systems due to a temperature difference. It is a form of energy that is often associated with temperature changes and can be added to or removed from a system. In the video, heat energy is represented by q and is used in the formula for calculating changes in internal energy. A positive q indicates heat added to the system, while a negative q indicates heat removed.
💡Work (w)
Work (w) is a measure of energy transfer that occurs when an object is moved by applying force along a displacement. In thermodynamics, work is done on or by a system and is a way of energy exchange. The sign convention in physics is such that positive work indicates work done by the system, while negative work indicates work done on the system. This concept is crucial in calculating changes in internal energy.
💡Sign Conventions
Sign conventions are standardized rules used in mathematics and physics to assign positive or negative values to quantities based on their direction or effect. In the context of the video, sign conventions are important for interpreting the values of heat energy (q) and work (w) in relation to the system. Positive values for q indicate heat added, while negative values indicate heat removed. For work, a positive value means work is done by the system, and a negative value means work is done on the system.
💡Mechanical Work
Mechanical work involves the application of force to an object causing it to move, resulting in energy transfer. In thermodynamics, mechanical work is one of the ways to change the internal energy of a system, the other being heat transfer. The video discusses how mechanical work is done on or by the system and how it affects the internal energy.
💡Thermal Expansion
Thermal expansion is the phenomenon where a material expands in volume or length due to an increase in temperature. This occurs because the particles within the material gain kinetic energy and move apart from each other. In the video, thermal expansion is implied when discussing the work performed by a gas expanding at a constant pressure.
💡Constant Pressure
Constant pressure refers to a condition where the pressure within a system remains unchanged during a process. This is a common scenario in thermodynamics, allowing for the calculation of work done under these conditions. The video discusses a gas expanding at a constant pressure and how this affects the work performed by or on the gas.
💡Work Formula
The work formula in thermodynamics is used to calculate the amount of work done under certain conditions, such as constant pressure. The formula is given by W = P × ΔV, where W is the work, P is the pressure, and ΔV is the change in volume. This formula is essential for determining the work done by or on a system when dealing with gases.
💡Gas Compression
Gas compression is the process of reducing the volume of a gas by applying an external force. This is the opposite of expansion and typically requires work to be done on the gas. In the video, gas compression is discussed in the context of calculating the work done on the gas when it is compressed at a constant pressure.
💡Energy Conservation
Energy conservation is the principle that the total energy in an isolated system remains constant, though it may change forms. This fundamental concept is central to the laws of thermodynamics and is used to analyze and solve problems involving heat, work, and internal energy. The video emphasizes the importance of energy conservation when calculating changes in internal energy and the work performed by or on a system.
Highlights

The problem discussed involves the calculation of the change in internal energy of a system.

The formula used for this calculation is ΔU = Q - W, where ΔU represents the change in internal energy, Q is the heat energy added or removed, and W is the work performed by or on the system.

This formula is associated with the first law of thermodynamics, which is the principle of conservation of energy.

There are two ways to change the internal energy of a system: by doing work on the system or by heat energy transfer.

In physics, a positive Q indicates heat energy is added to the system, while a negative Q indicates heat energy is removed.

A positive W in physics means work is done by the system, whereas a negative W means work is done on the system.

The sign conventions for Q and W are different in chemistry compared to physics.

In the first example, 300 joules of heat energy is added to the system (Q = +300 J), and the system performs 200 joules of work (W = +200 J).

The internal energy of the system in the first example increases by 100 joules (ΔU = +100 J).

In the second example, 700 joules of heat energy is removed from the system (Q = -700 J), and 400 joules of work is done on the system (W = -400 J).

The internal energy of the system in the second example decreases by 300 joules (ΔU = -300 J).

The third example involves a gas expanding at a constant pressure of 45,000 pascals, with the volume changing from 0.02 to 0.05 cubic meters.

The work performed by the gas in the third example is 1350 joules (W = +1350 J), calculated using the formula work = P × ΔV.

In the third example, 1500 joules of heat energy is added to the gas (Q = +1500 J), resulting in an increase of 150 joules in the internal energy (ΔU = +150 J).

The fourth example involves 2500 joules of heat energy being removed from a gas, and the gas is compressed at a constant pressure of 3 atm from 25 to 15 liters.

The work performed on the gas in the fourth example is -3039 joules (W = -3039 J), calculated by converting liters-atm to joules using the conversion factor.

The internal energy of the system in the fourth example increases by 539 joules (ΔU = +539 J) when considering both heat energy removal and work done on the gas.

Transcripts

Browse More Related Video

Internal Energy, Heat, and Work Thermodynamics, Pressure & Volume, Chemistry Problems

First Law of Thermodynamics, Basic Introduction - Internal Energy, Heat and Work - Chemistry

Thermodynamics and P-V Diagrams

Thermochemistry Equations & Formulas - Lecture Review & Practice Problems

First law of thermodynamics / internal energy | Thermodynamics | Physics | Khan Academy

Work from expansion | Thermodynamics | Physics | Khan Academy

Rate This

5.0 / 5 (0 votes)

Thanks for rating:

Related Tags
ThermodynamicsEnergyCalculationsHeatTransferWorkDonePhysicsPrinciplesInternalEnergyConservationOfEnergyMechanicalWorkHeatEnergyProblemSolving