Thermochemistry and Thermodynamic Principles: Key Concepts and Calculations

What is thermochemistry?

The study of heat transfer in chemical reactions and physical changes.

Define energy.

The ability to do work or transfer heat.

What is work in the context of energy?

Energy used to move an object.

How is heat defined?

Energy transfer accompanied by change in temperature.

What are the components of a thermodynamic system?

The system includes everything involved in the reaction or change observed.

What is meant by surroundings in thermodynamics?

Everything not in the system.

What constitutes the universe in thermodynamics?

The system and surroundings.

What is enthalpy?

Energy in a thermodynamic system.

What types of energy exist?

Potential energy and kinetic energy.

What is kinetic energy and how is it calculated?

Energy due to motion, calculated as KE = ½mv², where m is mass and v is velocity.

What is potential energy?

Energy due to position.

How can potential energy be converted?

It can be converted to kinetic energy and vice-versa.

What is the SI unit of energy?

The joule (J), equivalent to kg·m²/s².

If a 0.15 kg baseball is thrown at 88 mph, how is its kinetic energy calculated?

Convert speed to m/s and use KE = ½mv².

What is the kinetic energy of a 16-pound (7.25 kg) bowling ball thrown at 18 mph?

Calculate using KE = ½mv² with the appropriate conversion for speed.

What is the kinetic energy of a 150 lb person (68 kg) falling from a height of 6.1 m?

Calculate using KE = ½mv² at the impact speed of 10.9 m/s.

What is potential energy (PE) due to position?

Energy due to the position of an object relative to another position.

How is electrical potential energy (Eel) calculated?

Eel = k(Q1Q2)/d, where k is a constant, Q is charge, and d is distance.

What happens to Eel when Q1Q2 > 0 and distance increases?

Eel decreases as distance increases.

What happens to Eel when Q1Q2 < 0 and distance increases?

Eel increases as distance increases.

How is work (w) defined in physics?

w = Fd, where F is force and d is distance.

What is the unit of work in the SI system?

Joules (J), where 1 J = kg·m²/s².

What is the relationship between work and energy?

Work is often converted to potential or kinetic energy.

What is heat in the context of thermodynamics?

Energy transferred as a change in temperature.

What does higher temperature (T) indicate about a material?

Higher T corresponds to higher vibrational energy and more vibration.

Can heat be transferred without a change in temperature?

Yes, during phase changes.

What is the internal energy (E) of a system?

The sum of all kinetic and potential energies of everything in the system.

What does ∆E represent?

The change in internal energy, calculated as ∆E = Efinal - Einitial.

What is an exothermic process?

A process where the system's internal energy decreases (∆E < 0).

What is an endothermic process?

A process where the system's internal energy increases (∆E > 0).

How is energy exchanged between a system and its surroundings?

Through heat (q) and work (w), expressed as ∆E = q + w.

enthalpy (H) equation

Enthalpy is defined as H = E + PV, where E is internal energy, P is pressure, and V is volume.

How is the change in enthalpy (∆H) calculated at constant pressure?

∆H = ∆E + P∆V.

What is the significance of ∆H in a chemical reaction?

It represents the heat of reaction and can be exothermic (∆H < 0) or endothermic (∆H > 0).

What does specific heat (s) measure?

The energy required to raise the temperature of one gram of a substance by 1 K (1 °C).

What is the specific heat of liquid water?

s(H2O - liquid) = 4.184 J/g·K.

How is heat (q) calculated in a system at constant pressure?

q = sm∆T, where s is specific heat, m is mass, and ∆T is the change in temperature.

What is the relationship between heat and enthalpy at constant pressure?

At constant pressure, ∆H = q.

What is the difference between food calories and regular calories?

1 food cal (Cal) = 1000 cal.

What is the heat capacity of a bomb calorimeter used in experiments?

It is measured in kJ/°C and is used to calculate heat absorbed during reactions.

How do you calculate the enthalpy of a reaction?

∆Hr = Hfinal - Hinitial, or ∆Hr = Hproducts - Hreactants.

What is the formula for calculating heat (q) in relation to heat capacity and temperature change (∆T)?

q = (heat capacity)(∆T)

What type of function is enthalpy?

Enthalpy is a state function.

What does it mean that enthalpy is path-independent?

Enthalpy does not depend on the path taken to reach a particular state.

How can the enthalpy of a reaction be calculated?

By summing the enthalpies of a series of reactions that produce the same result.

What is Hess's Law?

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for individual steps.

What is the enthalpy of formation?

The enthalpy change when a compound is formed from its constituent elements in their standard states.

What are standard conditions for measuring enthalpy?

25 °C and 1.00 atmospheres of pressure.

What is the standard enthalpy of formation (∆Hf°) of a substance?

The enthalpy change when one mole of a compound is formed from its elements at standard conditions.

What is the enthalpy change (∆H°rxn) of a reaction?

The difference between the enthalpies of products and reactants.

What are the three phases of matter?

Solids, liquids, and gases.

What happens during a phase change?

Heat energy is exchanged, but the system temperature remains constant.

What is the enthalpy of fusion (∆Hfus)?

The heat required to melt a solid.

What is the enthalpy of vaporization (∆Hvap)?

The heat required to vaporize a liquid.

What is the relationship between ∆Hfus and ∆Hvap and their reverse processes?

∆Hfus and ∆Hvap are always greater than 0; their values are reversed for the reverse processes.

How do you calculate the heat of a phase change for a given amount of material?

Use the formula ∆H(kJ) = ∆Hphase change(kJ/mol) x material(mol).

What is the enthalpy change when 1.00 L of H2O evaporates if ∆Hvap = 40.66 kJ/mol?

Calculate using ∆H(kJ) = ∆Hvap(kJ/mol) x material(mol).

What is the enthalpy change when an Olympic swimming pool (2.6 x 10^6 L) of H2O freezes if ∆Hfus = 6.01 kJ/mol?

Calculate using ∆H(kJ) = ∆Hfus(kJ/mol) x material(mol).

What are the primary sources of food energy?

Carbohydrates, fats, and proteins.

What was the approximate worldwide human energy use in 2022?

Approximately 170 PWh (6.1 x 10^20 J).

What does it mean for a reaction's enthalpy to be found by decomposing reactants into elements?

It involves using standard enthalpy of formation values for the calculation.

What is the significance of the standard enthalpy of formation values?

They are required to calculate the enthalpy of a reaction based on reactants and products.

Why is the standard enthalpy of formation (∆Hf°) of diamond not equal to zero?

Because it is a compound formed from its elements, and its formation involves energy changes.