OIA1011 FIRST LAW OF THERMODYNAMICS & THERMOCHEMISTRY

What is the first law of thermodynamics?

Energy cannot be created or destroyed, only transformed; ΔU=Q+W, where ΔU is internal energy

What constitutes the total energy of a system?

E total=K.E.+P.E.+U, where K.E. is kinetic energy, P.E. is potential energy, and U is internal energy

Define internal energy.

The energy within a system due to molecular motion and interactions, including vibrational, rotational, electronic, and nuclear energies

What is the relationship between work and volume in thermodynamics?

A:W=−PΔV, where P is pressure and ΔV is the change in volume

What happens in a constant volume process?

ΔU=QV, since ΔV = 0 and no work is done

What is the equation for a constant pressure process?

ΔU=QP−PΔV , and ΔH=ΔU+PΔV, where ΔH is enthalpy

Define heat capacity (C).

The amount of heat required to raise the temperature of a substance by 1°C or 1 K; C=Q/ΔT

What is the difference between CP and CV?

CP is heat capacity at constant pressure; CV is heat capacity at constant volume

Why is CP>CV?

At constant pressure, the system does work on the surroundings, requiring additional heat

What is thermochemistry?

The study of heat changes in chemical and physical processes

What is the enthalpy of reaction (ΔH)?

The heat change at constant pressure; ΔH=ΣHproducts−ΣHreactants

What is the enthalpy of combustion?

The heat released when one mole of a substance is completely oxidized

What is the heat of combustion for glucose?

ΔH=−2801.65 KJ for C6H12O6

What is the enthalpy change for the reaction H2O (l)→H2O (g)

ΔH=+44.01 kJ/mol representing the enthalpy of vaporization

How is the enthalpy of formation calculated?

By measuring the enthalpy change when one mole of a compound forms from its elements in their standard states

What does Hess's law state?

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

Provide an example of Hess's law in action.

For C (graphite)+12O2→CO, the enthalpy is derived by subtracting two known combustion reactions

What is Kirchoff’s equation?

ΔH2−ΔH1=ΔCP(T2−T1), used to calculate enthalpy changes at different temperatures

What is the enthalpy of reaction for N2+O2→NO at 558K?

ΔH=90.53 kJ

What is bond enthalpy?

The energy required to break one mole of a specific bond in a molecule

Estimate the enthalpy of combustion for methane using bond enthalpies.

ΔH=−634.4 kJ, calculated from bond energies of reactants and products

How does a bomb calorimeter work?

It measures heat changes at constant volume to determine ΔU

hy is ΔH\Delta H approximately equal to ΔU\Delta U for reactions in solution?

PΔV is negligible for liquid-phase reactions

What is the enthalpy change for the combustion of carbon to form carbon dioxide?

ΔH=−393.51 kJ/mol

How is spontaneity determined from enthalpy and entropy?

By Gibbs free energy: ΔG=ΔH−TΔS, ΔG<0 indicates spontaneity

What does a negative ΔH signify?

The reaction is exothermic and releases heat

What does a positive ΔH signify?

The reaction is endothermic and absorbs heat

How does temperature affect reaction enthalpy?

Higher temperatures increase ΔH for endothermic reactions due to heat absorption

Why are enthalpies of elements in their standard states zero?

To simplify calculations as the reference point

What is the relationship between heat, work, and internal energy?

ΔU=Q+W; internal energy changes reflect heat absorbed/released and work done