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GOB Chemistry - Thermochemistry Key Concepts

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Terms in this set (22)

  • What is energy?

    Energy is the ability to do work or transfer heat.

  • Define kinetic energy.

    Kinetic energy is the energy an object possesses due to its motion, given by \(E_k=\frac{1}{2}mv^2\).

  • What is potential energy in chemistry?

    Potential energy is energy due to an object's position or chemical composition, especially electrostatic potential energy \(E_{el} = \frac{kQ_1Q_2}{d}\).

  • What are the SI and non-SI units of energy?

    The SI unit is the joule (J). The calorie (cal) is a non-SI unit where 1 cal = 4.184 J.

  • What is the first law of thermodynamics?

    Energy is neither created nor destroyed; total energy of the universe is constant. Energy lost by the system is gained by the surroundings, and vice versa.

  • Define internal energy (E) of a system.

    Internal energy is the sum of all kinetic and potential energies of the system's components.

  • How is change in internal energy (ΔE) calculated?

    ΔE = E_final − E_initial; it represents energy absorbed or released by the system.

  • What is the relationship between ΔE, heat (q), and work (w)?

    ΔE = q + w, where q is heat exchanged and w is work done on or by the system.

  • What is the sign convention for q, w, and ΔE?

    q > 0 means system gains heat; w > 0 means work done on system; ΔE > 0 means net gain of energy by system.

  • What is the difference between endothermic and exothermic processes?

    Endothermic: heat absorbed, ΔH > 0. Exothermic: heat released, ΔH < 0.

  • What is a state function? Is internal energy a state function?

    A state function depends only on the current state, not the path taken. Internal energy (E) is a state function.

  • Is heat (q) a state function?

    No, heat (q) and work (w) are path-dependent and not state functions.

  • How is work done by a gas during expansion or compression calculated?

    Work done, w = −PΔV, where P is pressure and ΔV is volume change.

  • Define enthalpy (H).

    Enthalpy is H = E + PV, the internal energy plus pressure-volume product.

  • What is the relationship between ΔH and heat at constant pressure?

    At constant pressure, ΔH = q_p, the heat gained or lost by the system.

  • How is enthalpy of reaction (ΔH) calculated?

    ΔH = H_products − H_reactants; it represents heat change during a chemical reaction.

  • What is calorimetry?

    Calorimetry is the measurement of heat flow during chemical reactions or physical changes.

  • Define specific heat capacity (C_s).

    Specific heat is the energy required to raise 1 g of a substance by 1 K (or 1 °C).

  • How is heat (q) calculated using specific heat?

    q = m × C_s × ΔT, where m is mass, C_s is specific heat, and ΔT is temperature change.

  • What is Hess's Law?

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

  • What is the standard enthalpy of formation (ΔH_f°)?

    ΔH_f° is the enthalpy change when 1 mole of a compound forms from its elements in their standard states.

  • How to calculate ΔH for a reaction using standard enthalpies of formation?

    ΔH = Σ nΔH_f°(products) − Σ mΔH_f°(reactants), where n and m are stoichiometric coefficients.