EmSAT Chemistry Flashcards

What does Le Chatelier's principle state?

Answer: A system at equilibrium will shift to counteract a stress applied to it

Le Chatelier's principle states that if a stress (change in concentration, temperature, or pressure) is applied to a system at equilibrium, the system will shift in the direction that partially counteracts that stress.

What is the Kc expression for: N₂ + 3H₂ ⇌ 2NH₃?

Answer: Kc = [NH₃]² / [N₂][H₂]³

Kc = [products]^coefficients / [reactants]^coefficients = [NH₃]² / ([N₂][H₂]³). Each concentration is raised to the power of its stoichiometric coefficient.

What is an endothermic reaction?

Answer: A reaction that absorbs heat from the surroundings

An endothermic reaction absorbs heat energy from the surroundings. The products have higher energy than the reactants, and the enthalpy change (ΔH) is positive.

What is enthalpy (H) in thermodynamics?

Answer: The heat content of a system at constant pressure

Enthalpy is the heat content of a thermodynamic system at constant pressure. The change in enthalpy (ΔH) indicates whether a reaction releases (exothermic) or absorbs (endothermic) heat.

What is Hess's Law?

Answer: The total enthalpy of a reaction is independent of the pathway

Hess's Law states that the total enthalpy change for a reaction is the same regardless of whether it occurs in one step or multiple steps. Enthalpy is a state function.

What is the standard enthalpy of combustion?

Answer: Heat released when 1 mole of substance completely burns in oxygen

Standard enthalpy of combustion (ΔHc°) is the enthalpy change when one mole of a substance completely combusts in excess oxygen under standard conditions. It is always exothermic (negative ΔH).