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General Chemistry: Energy, Thermodynamics, and Calorimetry

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  • What is kinetic energy?

    Kinetic energy is the energy associated with the motion of an object.

  • What is potential energy?

    Potential energy is the energy associated with the position or arrangement of an object.

  • Write the expression for the change in energy (ΔE) of a system losing heat and doing work on the surroundings.

    \(\Delta E = q + w\), where both \(q\) (heat) and \(w\) (work) are negative since the system loses heat and does work.

  • What is the sign convention for heat (q) and work (w) when the system loses energy?

    Heat lost by the system: \(q < 0\). Work done by the system: \(w < 0\).

  • Formula relating heat (q), mass (m), specific heat capacity (c), and temperature change (ΔT).

    \(q = m c \Delta T\)

  • How to calculate specific heat capacity (c) from heat, mass, and temperature change?

    \(c = \frac{q}{m \Delta T}\)

  • Convert 59.3 kJ to Joules.

    59.3 kJ = 59300 J (since 1 kJ = 1000 J).

  • Calculate the temperature change if temperature rises from 298 K to 398 K.

    \(\Delta T = 398 - 298 = 100\ K\)

  • How to calculate moles of ethanol burned from mass and molar mass?

    \(\text{moles} = \frac{\text{mass}}{\text{molar mass}}\)

  • Given ethanol mass 21.8 g and molar mass 46.07 g/mol, calculate moles of ethanol.

    \(\frac{21.8}{46.07} \approx 0.473\ mol\)

  • How to calculate heat released by a reaction from moles and enthalpy change?

    \(q = \text{moles} \times \Delta H^{\circ}_{rxn}\)

  • What is the relationship between heat absorbed by the calorimeter and heat released by the reaction?

    Heat absorbed by calorimeter equals the negative of heat released by the reaction: \(q_{cal} = -q_{rxn}\).

  • Formula to calculate heat absorbed by calorimeter from heat capacity and temperature change.

    \(q_{cal} = C_{cal} \Delta T\)

  • How to find calorimeter heat capacity (C_cal) from heat released and temperature change?

    \(C_{cal} = \frac{q_{cal}}{\Delta T}\)

  • Calculate moles of PCl3 from 612 g and molar mass 137.32 g/mol.

    \(\frac{612}{137.32} \approx 4.46\ mol\)

  • How to calculate reaction equivalents for PCl3 given balanced equation 4 PCl3 → products?

    Reaction equivalents = \(\frac{\text{moles of PCl3}}{4}\)

  • Calculate energy required for decomposition using reaction equivalents and ΔH°rxn.

    \(\text{Energy} = \text{reaction equivalents} \times \Delta H^{\circ}_{rxn}\)

  • What is the enthalpy change (ΔH°rxn) for the decomposition of PCl3?

    \(+1207\ kJ\) per 4 moles of PCl3 decomposed.

  • What does a positive ΔH°rxn indicate about a reaction?

    A positive ΔH°rxn means the reaction is endothermic, absorbing energy.

  • What does a negative ΔH°rxn indicate about a reaction?

    A negative ΔH°rxn means the reaction is exothermic, releasing energy.