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

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40 Terms

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Energy

The capacity to do work or transfer heat.

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Work (w)

Energy used to cause an object with mass to move.

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Heat (q)

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

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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.

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Calorie (cal)

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

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Thermodynamics

The study of energy and its transformations.

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Thermochemistry

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

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Law of Conservation of Energy

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

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System

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

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Surroundings

Everything outside the system that can exchange energy with it.

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Internal Energy (ΔU)

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

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Endothermic Process

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

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Exothermic Process

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

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Thermal Equilibrium

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

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Heat Capacity (C)

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

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Specific Heat Capacity (c or Cp)

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

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Molar Heat Capacity (Cm)

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

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Heat-Transfer Equation

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

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First Law of Thermodynamics

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

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Sign Convention – Heat

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

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Sign Convention – Work

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

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Calorimetry

Experimental measurement of heat changes in physical or chemical processes.

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Constant-Pressure Calorimeter

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

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Bomb Calorimeter

Constant-volume device used to determine heats of combustion.

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Enthalpy (H)

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

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Enthalpy of Reaction (ΔHrxn)

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

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Standard Enthalpy Change (ΔH°)

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

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Standard Enthalpy of Formation (ΔHf°)

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

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Enthalpy of Combustion (ΔHcomb)

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

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Enthalpy of Vaporization (ΔHvap)

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

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Enthalpy of Fusion (ΔHfus)

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

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Thermochemical Equation

Balanced chemical equation that includes the associated enthalpy change.

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Hess’s Law

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

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Heat of Combustion (qrxn)

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

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Coffee-Cup Calorimeter

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

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Thermal Insulation

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

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Heat Capacity of Metals

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

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State Function

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

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Pressure-Volume Work

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

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Standard State

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