Thermochemistry

Variable depending on the element

+50 kJ/mol

-100 kJ/mol

0 kJ/mol

It involves no net change in energy since it's at equilibrium.

It requires an input of energy and is endothermic.

It releases energy and is likely exothermic.

It increases entropy without releasing or absorbing heat substantially.

Dichloromethane ( CH2Cl2) only considering its lower boiling point than reactants'.

CH3Cl + HCl due to activation energy barriers despite thermodynamic favorability.

Carbon disulfide (CS2) since it does not form under these conditions at all.

CH4(l) + Cl2(l) as they condense together under cooler conditions.

Differences in types within chemical bonding of reactants

Presence of catalysts in the reaction mixture

Slight variations in molecular shapes

Magnitude of coefficients in the stoichiometric equation

Dissolving salt leads to increased boiling elevation, not affecting the freezing level significantly.

Adding salt results in decreased vapor pressure, thus lowering the freezing temperature.

Addition NaCl increases the solution's ionic concentration, causing a greater freezing point depression.

Introduction of extra ions via sodium chloride does not change the number of solute particles present, therefore fails to alter phase transition points drastically.

The difference between products and reactants' enthalpies.

The heat change associated with the formation reaction.

The ambient temperature outside a laboratory setting.

The standard state of other elements and compounds involved.

The formation of gaseous ammonia (NH$_{3}$(g)) from nitrogen gas (N$_{2}$(g)) and hydrogen gas (H$_{2}$(g)).

The synthesis of liquid ethanol (C$_{2}$H$_{5}$OH(l)) from carbon dioxide (CO$_{2}$(g)) and hydrogen gas (H$_{2}$(g)).

The combustion of methane (CH$_{4}$(g)) to produce carbon dioxide (CO$_{2}$(g)) and water vapor (H$_{2}$O(g)).

The dissolution of sodium hydroxide pellets (NaOH(s)) in water.

X forms stronger bonds due to better overlap with orbitals from other atoms in compounds it forms.

X has greater atomic radius reducing effective nuclear charge on bonding electrons.

Y exhibits stronger Van der Waals forces causing less compact structures in its compounds.

Y has higher ionization energy making its compounds less stable energetically.

The element has a coefficient corresponding to its atomic number.

The element appears without any coefficient or subscript.

The element has subscripts indicating physical phase (e.g., s, l, g).

The element appears with superscripts denoting isotopic composition.

Standard enthalpy of formation

Activation energy for a reaction

Heat capacity at constant volume

Change in heat during a phase transition