1. Commonly used terms in thermodynamics:
- System: The part of the universe that is under study.
- Surroundings: Everything else in the universe except the system.
- State Variables: Properties that describe the state of a system (e.g., pressure, volume, temperature).
- Equilibrium: A state in which all state variables are unchanging.
- Heat: Energy transferred due to a temperature difference.
- Work: Energy transferred by any process other than heat.

2. Exothermic vs Endothermic Reactions:
- Exothermic reactions release heat to the surroundings (ΔH is negative).
- Endothermic reactions absorb heat from the surroundings (ΔH is positive).

3. First Law of Thermodynamics: Energy cannot be created or destroyed, only transferred or converted from one form to another. Mathematically, ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.

4. Internal Energy: The total energy contained within a system. It includes kinetic energy (due to motion of particles) and potential energy (due to intermolecular forces).

5. Enthalpy and Enthalpy Change:
- Enthalpy (H) is a state function that accounts for heat flow in processes occurring at constant pressure. It is related to the internal energy U by the equation H = U + PV.
- Enthalpy Change (ΔH) is the amount of energy absorbed by or released from a system as heat during a process at constant pressure.

6. Relationship between Enthalpy Change and Internal Energy Change: ΔH = ΔU + PΔV, where P is the constant pressure and ΔV is the change in volume.

7. Definitions of Specific Enthalpies:
- Formation: The enthalpy change when one mole of a compound is formed from its elements in their standard states.
- Combustion: The enthalpy change when one mole of a substance is completely burned in oxygen.
- Neutralisation: The enthalpy change when one mole of water is formed from the reaction of an acid and a base.
- Atomisation: The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
- Transition: The enthalpy change when a solid changes to a liquid or a liquid to a gas.
- Solution: The enthalpy change when one mole of a solute is dissolved in a solvent.
- Ionisation: The enthalpy change when one mole of gaseous atoms is converted into ions.

8. Relationship between Enthalpy of Reaction and Enthalpies of Formation: The enthalpy change for a reaction is equal to the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants (Hess's Law).

Question

1. Commonly used terms in thermodynamics:
   - System: The part of the universe that is under study.
   - Surroundings: Everything else in the universe except the system.
   - State Variables: Properties that describe the state of a system (e.g., pressure, volume, temperature).
   - Equilibrium: A state in which all state variables are unchanging.
   - Heat: Energy transferred due to a temperature difference.
   - Work: Energy transferred by any process other than heat.

2. Exothermic vs Endothermic Reactions:
   - Exothermic reactions release heat to the surroundings (ΔH is negative).
   - Endothermic reactions absorb heat from the surroundings (ΔH is positive).

3. First Law of Thermodynamics: Energy cannot be created or destroyed, only transferred or converted from one form to another. Mathematically, ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system.

4. Internal Energy: The total energy contained within a system. It includes kinetic energy (due to motion of particles) and potential energy (due to intermolecular forces).

5. Enthalpy and Enthalpy Change:
   - Enthalpy (H) is a state function that accounts for heat flow in processes occurring at constant pressure. It is related to the internal energy U by the equation H = U + PV.
   - Enthalpy Change (ΔH) is the amount of energy absorbed by or released from a system as heat during a process at constant pressure.

6. Relationship between Enthalpy Change and Internal Energy Change: ΔH = ΔU + PΔV, where P is the constant pressure and ΔV is the change in volume.

7. Definitions of Specific Enthalpies:
   - Formation: The enthalpy change when one mole of a compound is formed from its elements in their standard states.
   - Combustion: The enthalpy change when one mole of a substance is completely burned in oxygen.
   - Neutralisation: The enthalpy change when one mole of water is formed from the reaction of an acid and a base.
   - Atomisation: The enthalpy change when one mole of gaseous atoms is formed from the element in its standard state.
   - Transition: The enthalpy change when a solid changes to a liquid or a liquid to a gas.
   - Solution: The enthalpy change when one mole of a solute is dissolved in a solvent.
   - Ionisation: The enthalpy change when one mole of gaseous atoms is converted into ions.

8. Relationship between Enthalpy of Reaction and Enthalpies of Formation: The enthalpy change for a reaction is equal to the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants (Hess's Law).

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