Energy and Thermochemistry

These flashcards cover key concepts related to energy, thermochemistry, and thermodynamic principles as discussed in the lecture.

What is energy?

The capacity to do work or to transfer heat.

What are the two main types of energy in this context?

Work (energy used to cause an object with mass to move) and heat (energy used to cause the temperature of an object to increase).

What is the unit for energy?

Joule (J), derived from kinetic energy of a 2\ kg mass moving at 1\ m/s.

How is heat capacity defined?

The amount of heat required to raise an object's temperature by 1\ K (or 1°C).

What is the formula for calculating heat (q) gained or lost?

q = mCp\Delta T, where m is mass, Cp is specific heat capacity, and \Delta T is the temperature change.

What is the first law of thermodynamics?

Energy can neither be created nor destroyed; it can only be converted from one form to another.

What is an endothermic reaction?

A reaction where heat is transferred from the surroundings to the system, resulting in a decrease in energy for the surroundings.

What is an exothermic reaction?

A reaction where heat is transferred from the system to the surroundings, resulting in a decrease in energy for the system.

How do you define the system and surroundings in thermodynamics?

The system is the small area of interest, and the surroundings are everything else.

What does thermal equilibrium mean?

It is the state reached when two objects at different temperatures exchange heat until they are at the same temperature.

What is enthalpy?

A thermodynamic quantity that accounts for heat flow at constant pressure, expressed as H = U + PV.

How is the change in internal energy (\Delta U) calculated?

\Delta U = q + w, where q is heat transferred and w is work done.

What is Hess's Law?

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

What are state functions in thermodynamics?

Properties of a system determined by its current state, such as temperature, pressure, and volume, independent of the path taken to reach that state.

What does \Delta H_{rxn} represent?

The enthalpy change for a chemical reaction determined as the difference between the enthalpy of products and reactants.

How do you calculate \Delta H for a reaction?

\Delta H{rxn} = \sum \Delta H{products} - \sum \Delta H_{reactants}.

What is a thermochemical reaction?

A reaction where heat changes, such as combustion, are involved in the chemical change.

What does the term 'specific heat capacity' refer to?

The amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

How is pressure-volume work (w) calculated?

w = -P\Delta V, where P is the external pressure and \Delta V is the change in volume.

What are the sign conventions for work (w)?

• w > 0: Work is done on the system by the surroundings (compression).
• w < 0: Work is done by the system on the surroundings (expansion).

What is the standard enthalpy of formation (\Delta H_f^\circ)?

The enthalpy change for the formation of one mole of a substance from its constituent elements in their most stable states under standard conditions.

What is the value of \Delta H_f^\circ for an element in its standard state?

The standard enthalpy of formation for any element in its most stable form is defined as 0\ kJ/mol.

How is molar heat capacity different from specific heat capacity?

Molar heat capacity is the heat required to raise the temperature of one mole of a substance by 1\ K, while specific heat capacity is per one gram.

What is the difference between constant-pressure and constant-volume calorimetry?

1. Constant-pressure (q_p): Measures \Delta H (e.g., coffee-cup calorimeter).
2. Constant-volume (q_v): Measures \Delta U (e.g., bomb calorimeter).

What is the conversion factor between liter-atmospheres and Joules?

1\ L\cdot atm = 101.325\ J.