5.1

A set of vocabulary flashcards covering the essential terms and definitions from the lecture on Energy and Thermochemistry.

Energy

The capacity to do work or transfer heat.

Work (w)

Energy used to cause an object with mass to move.

Heat (q)

Energy transferred because of a temperature difference; causes temperature change in an object.

Joule (J)

SI unit of energy equal to the kinetic energy of a 2 kg mass moving at 1 m s⁻¹; 1 J = 1 kg·m²·s⁻².

Calorie (cal)

Amount of energy needed to raise the temperature of 1 g of water by 1 °C; 1 cal = 4.184 J.

Thermodynamics

The study of energy and its transformations.

Thermochemistry

Branch of thermodynamics that examines the heat flow accompanying chemical reactions.

Law of Conservation of Energy

Energy cannot be created or destroyed, only converted from one form to another.

System

The specific part of the universe chosen for study in a thermodynamic analysis.

Surroundings

Everything outside the system that can exchange energy with it.

Internal Energy (ΔU)

Sum of all kinetic and potential energy of the particles in a system; ΔU = q + w.

Endothermic Process

Process in which heat is absorbed by the system from the surroundings; system energy increases.

Exothermic Process

Process in which heat is released by the system to the surroundings; system energy decreases.

Thermal Equilibrium

Condition in which two objects at different temperatures reach the same temperature and no net heat flows.

Heat Capacity (C)

Quantity of heat required to raise the temperature of an object by 1 K (or 1 °C).

Specific Heat Capacity (c or Cp)

Heat required to raise the temperature of 1 g of a substance by 1 K (or 1 °C).

Molar Heat Capacity (Cm)

Heat required to raise the temperature of 1 mol of a substance by 1 K.

Heat-Transfer Equation

q = m c ΔT, where m is mass, c is specific heat capacity, and ΔT is Tfinal – Tinitial.

First Law of Thermodynamics

ΔU = q + w; energy change of a system equals heat added plus work done on the system.

Sign Convention – Heat

q > 0 when heat is absorbed by the system; q < 0 when heat is released.

Sign Convention – Work

w > 0 when work is done on the system; w < 0 when work is done by the system.

Calorimetry

Experimental measurement of heat changes in physical or chemical processes.

Constant-Pressure Calorimeter

Coffee-cup calorimeter that operates at constant pressure to measure enthalpy changes (ΔH).

Bomb Calorimeter

Constant-volume device used to determine heats of combustion.

Enthalpy (H)

State function defined as H = U + PV; at constant pressure, heat flow equals ΔH.

Enthalpy of Reaction (ΔHrxn)

Heat change accompanying a chemical reaction at constant pressure; ΔHrxn = Hproducts – Hreactants.

Standard Enthalpy Change (ΔH°)

Enthalpy change when reactants and products are in their standard states (1 atm, 25 °C).

Standard Enthalpy of Formation (ΔHf°)

Enthalpy change for forming 1 mol of a compound from its elements in their standard states.

Enthalpy of Combustion (ΔHcomb)

Enthalpy change when 1 mol of a substance burns completely in oxygen.

Enthalpy of Vaporization (ΔHvap)

Enthalpy change for converting a liquid to a gas at constant pressure.

Enthalpy of Fusion (ΔHfus)

Enthalpy change for converting a solid to a liquid at constant pressure.

Thermochemical Equation

Balanced chemical equation that includes the associated enthalpy change.

Hess’s Law

The total enthalpy change for a reaction is the same whether it occurs in one step or several steps.

Heat of Combustion (qrxn)

Quantity of heat released when a substance undergoes complete combustion, usually measured in a bomb calorimeter.

Coffee-Cup Calorimeter

Simple, insulated constant-pressure calorimeter often made of nested Styrofoam cups.

Thermal Insulation

Property of a calorimeter that prevents heat exchange with the external environment.

Heat Capacity of Metals

Most metals have molar heat capacities near 25 J mol⁻¹ K⁻¹.

State Function

Property that depends only on the current state of a system, not on the path taken (e.g., H, U, P, V).

Pressure-Volume Work

Work associated with volume changes against an external pressure; w = −PΔV at constant external pressure.

Standard State

Reference state of a substance at 1 atm pressure and 25 °C used for tabulating thermodynamic data.