kech105 (1)

It does not require detailed knowledge of the motion of each particle; instead, it deals with average measurable properties.

Heat transfer, work done on or by the system, or matter entering or leaving the system.

∆U = q + w.

Extensive properties depend on the amount of substance, while intensive properties do not.

Doing mechanical work increases the temperature of the system, as shown by the change from temperature T_A to T_B.

By multiplying the specific heat (c) of the substance by the mass (m) and the change in temperature (∆T).

No work is done (w = 0).

44.01 kJ.

Pressure (p), volume (V), temperature (T), and composition.

The conservation of energy and its mathematical expression.

∆H = ∆U = qV when ∆V = 0.

By monitoring the temperature rise, where q = C ∆T.

∆H is the heat absorbed or evolved at constant pressure, also known as the heat of reaction or enthalpy of reaction, ∆rH.

Its most stable state of aggregation at 25°C and 1 bar pressure.

q = -w.

Calorimetry.

It can do mechanical work or provide electrical energy.

When a system is in equilibrium or moves between equilibrium states.

A reversible process is one that can be reversed by an infinitesimal change and proceeds through a series of equilibrium states.

∆H is positive for endothermic reactions which absorb heat.

37.904 kJ mol-1.

∆fH°.

An isolated system has no exchange of energy or matter between the system and its surroundings.

Properties such as pressure (p), volume (V), temperature (T) that depend only on the state of the system.

The total energy of the system, which may include chemical, electrical, mechanical, or other forms of energy.

The heat absorbed by the system at constant pressure.

A system where there is no exchange of matter, but energy can be exchanged with the surroundings.

p∆V = ∆ngRT, where ∆ng is the change in the number of moles of gas.

Joule concluded that a given amount of work done on a system produces the same change of state, as measured by temperature change, regardless of the method used.

The heat capacity at constant volume.

H = U + pV.

The negative sign indicates the exothermic nature of the reaction.

Because ∆ng = 0, meaning there is no change in the number of moles of gas during the reaction.

The presence of reactants in a thermos flask or any closed insulated vessel.

The work done is positive since (V_f - V_i) is negative, and negative multiplied by negative gives positive.

A system where there is an exchange of energy and matter with the surroundings.

A principle used to calculate enthalpy changes.

We can only measure the changes in internal energy, ∆U of the system.

Enthalpy H is useful for reactions at constant atmospheric pressure.

Mechanical work, specifically pressure-volume work.

Some familiar state functions include volume (V), pressure (p), and temperature (T).

Δ vap H° = +40.79 kJ mol⁻¹.

Thermodynamics.

The separation between the system and the surroundings.

The shaded area represents the work done on the gas.

Because solids and liquids do not undergo significant volume changes upon heating.

C is called the heat capacity.

The internal energy U is defined such that the adiabatic work required to change the state of the system is equal to the difference in internal energy between two states (∆U = U_2 - U_1 = w_ad).

The heat capacity at constant pressure.

C graphite for carbon and S rhombic for sulfur.

Everything other than the system.

There is no transfer of heat between the system and its surroundings.

Properties like internal energy (U) and enthalpy (H).

By a set of Cartesian coordinates specifying a particular volume in space.

The amount of heat required to raise the temperature of one unit mass of a substance by one degree Celsius (or one Kelvin).

The expansion of a gas in a vacuum where no work is done.

H2 gas for dihydrogen and O2 gas for dioxygen.

Internal energy can be changed by transferring heat (q) from the surroundings to the system or vice-versa without doing work.

The enthalpy change is -20.7 kJ for the combustion of 1g of graphite.

195 K.

The strength of the intermolecular interactions in the substance undergoing the phase transformations.

w = -p_ex ΔV = -p_ex (V_f - V_i), where ΔV = V_f - V_i.

How to determine the energy changes involved in a chemical reaction.

∆H is negative for exothermic reactions which evolve heat.

∆H = ∆U + ∆ng RT, or ∆U = ∆H - ∆ng RT.

Using the equation ∆H = ∆U + ∆ngRT.

∆U = q - w, indicating a closed system.

In an endothermic reaction, heat is absorbed, so qp is positive and ∆rH is also positive.

Extensive properties include mass, volume, and heat capacity; intensive properties include temperature, density, and pressure.

Chemical energy.

The part of the universe in which observations are made.

Pressure and temperature.

Closed, open, and isolated systems.

It depends only on the initial and final states of the system, not on how the change is carried out.

A state function that is associated with the spontaneity of processes.

∆U = -q, with thermally conducting walls.

In an exothermic reaction, heat is evolved, so qp is negative and ∆rH is also negative.

If p_ex is greater than the internal pressure (p), the piston moves inward, doing work on the gas.

Substances are in their pure form at 1 bar and a specified temperature, usually 298 K.

It indicates that work is done on the system during compression.

The external pressure p_ex is always infinitesimally greater than the pressure of the gas.

Reactants in an open beaker.

The law of conservation of energy; energy can neither be created nor destroyed.

Irreversible processes.

That one mole of the compound has been formed in its standard state from its elements.

Extensive properties depend on the quantity of matter, while intensive properties do not.

C_p - C_V = R, where R is the ideal gas constant.

Changes in enthalpy (∆H) are measured.

The transformations of energy in macroscopic systems.

It is calculated as w = -Σ p ΔV.

A process in which heat transfer does not occur between the system and surroundings.

If w = 0 and q = 0, then ∆U = 0.

It indicates the spontaneity of a reaction and relates to the equilibrium constant.

By using the equation w_rev = ∫(p_ext dV).

ΔH = [Hm (CO2, g) + 2 Hm (H2O, l)] – [Hm (CH4, g) + 2 Hm (O2, g)]

q = -CV × ∆T, where q is the heat from the reaction mixture and CV is the heat capacity of the calorimeter.

The value of an extensive property per mole of substance.

The direct conversion of a solid into its vapor.

Equal amount of heat is given off to the surroundings as the process is reversed.

Energy changes of macroscopic systems.

The universe = The system + The surroundings.

In an expansion process, the external pressure p_ex is less than the internal pressure p_in.

Reactants in a closed vessel made of conducting material (e.g., copper or steel).

∆U = w, and the wall is adiabatic.

The increase in temperature is proportional to the heat transferred.

The internal energy of the system increases and is considered positive when work is done on it.

-13.56 kJ mol⁻¹.

The temperature remains the same, demonstrating that temperature is an intensive property.

At constant volume (q_V) and at constant pressure (q_p).

Δ sub H° = 25.2 kJ mol⁻¹.

The value of ΔrH° is reversed in sign.

ΔfH° = –285.8 kJ mol–1.

The heat capacity for one mole of a substance, representing the quantity of heat needed to raise the temperature of one mole by one degree Celsius (or Kelvin).

The enthalpy change for a reaction when all substances are in their standard states.

Because it depends on state functions U, p, and V, which are independent of path.

Negligible change in volume, therefore p∆v = 0.

It is converted to q_V using the known heat capacity of the calorimeter.

Using the formula w = 2.303 nRT log(V_f/V_i).

ΔrH° = Σ a_i ΔfH°(products) - Σ b_i ΔfH°(reactants).

The pure form of the substance at a specified temperature and 1 bar.

A calorimeter.

IUPAC recommends that q is positive when heat is transferred into the system and negative when heat is transferred out of the system.

∆H = ∆U = -13.56 kJ mol⁻¹.

44.01 kJ.

ΔfH° = –36.4 kJ mol–1.

The internal energy of the system increases, and q is considered positive in this case.

Melting is endothermic, requiring heat, with all enthalpies of fusion being positive.

To ensure that no heat is lost to the surroundings.

The total enthalpy change for a reaction is the sum of the enthalpy changes of the individual steps.

The amount of heat required to vaporize one mole of a liquid at constant temperature and under standard pressure (1 bar).

The heat absorbed by the system can be measured in terms of the temperature difference (T_B - T_A) when heat is transferred through thermally conducting walls.

–285.83 kJ mol–1.

The enthalpy change varies with the amount of substance involved in the reaction.

It is the enthalpy change when one mole of a compound is formed from its constituent elements.

It indicates that the reaction releases heat (exothermic).

The enthalpy change that accompanies the melting of one mole of a solid substance in standard state.

q = -w = p_ext (V_f - V_i).

ΔfusH° = 6.00 kJ mol–1.

8 litre-atm.

Δ H1 = -7560 J mol⁻¹ = -7.56 kJ mol⁻¹.

w_rev = -nRT ln(V_f/V_i).

Using a bomb calorimeter.

It is required to plan the heating or cooling to maintain constant temperature.

Δ vap U = 41.53 kJ.

To determine the enthalpy change for a chemical reaction.

No work is done (w = 0).

Because the intermolecular dipole-dipole interactions in acetone are significantly weaker than the strong hydrogen bonds in water.

Δ H = Δ H1 + Δ H2 = -7.56 kJ + (-6.00 kJ) = -13.56 kJ.

They refer to the number of moles of reactants and products involved in the reaction.

∆rH = (sum of enthalpies of products) - (sum of enthalpies of reactants).

∆U = 0.

Δ vap U = Δ vap H° - pΔV = Δ vap H° - ΔngRT.

ΔrH° = 178.3 kJ mol–1, indicating it is an endothermic process.

ΔfH1° = 3(–285.83 kJ mol–1) - 1(–824.2 kJ mol–1).

q = 0.

By reversing the original equation and changing the sign of ΔrH°.

∆U = q_V.

–393.5 kJ mol–1.

6.00 kJ mol⁻¹.

It is not directly measurable but can be calculated using related reactions.

It indicates that the reaction is exothermic.

A balanced chemical equation that includes the value of ΔrH°.