Chemistry Enthalpy and Reaction Quiz

Neutralization reaction is a reaction between an acid and a base, producing salt and water. For example, hydrochloric acid (HCl) and sodium hydroxide (NaOH) react to form sodium chloride (NaCl) and water (H2O).

In a titration, the equivalence point is the point at which the moles of acid are equal to the moles of base. This is usually indicated by a color change in an indicator.

The molar mass of a molecule is the mass of one mole of the molecule. For example, the molar mass of water is 18.015 g/mol. In this calculation, molar mass is equal to the mass of the acid divided by the number of moles of NaOH used to neutralize it.

The percentage purity of a substance is the mass of the pure substance divided by the total mass of the sample multiplied by 100%. For example, if a 10 g sample of iron contains 8 g of pure iron, the percentage purity is 80%.

The heat of reaction is the amount of heat absorbed or released during a chemical reaction. An endothermic reaction absorbs heat from the surroundings, while an exothermic reaction releases heat to the surroundings.

The heat capacity of a calorimeter is the amount of heat required to raise the temperature of the calorimeter by 1 degree Celsius. When an endothermic reaction takes place in a calorimeter, the temperature of the water bath decreases. The amount of heat absorbed by the reaction can be calculated by subtracting the heat absorbed by the calorimeter from the total heat absorbed by the system.

Titration is a technique for determining the concentration of a solution by reacting it with a solution of known concentration. The unknown solution is gradually added to the known solution until the reaction reaches a point of equivalence.

Indicators change color at a specific pH. This allows them to be used to signal the equivalence point of a titration. Different indicators are suited for different types of titrations based on the pH range of the reaction.

The enthalpy change that occurs when one mole of a compound is formed from its elements in their standard states.

The energy required to break one mole of a specific bond in a gaseous molecule, forming two gaseous atoms.

The enthalpy change that occurs when one mole of a substance is completely burned in excess oxygen under standard conditions.

The energy required to break one mole of bonds between atoms in a substance, forming gaseous atoms.

The enthalpy change that occurs when one mole of a substance changes from its standard state to its gaseous state under standard conditions.

A reaction that occurs without the need for external energy input. The change in Gibbs free energy is negative.

The change in Gibbs free energy (∆G) is negative, indicating that a reaction is spontaneous at that temperature.

The change in Gibbs free energy (∆G) is positive, indicating that a reaction is non-spontaneous at that temperature.

The equilibrium constant (Keq) is a value that indicates the relative amounts of reactants and products present at equilibrium. It is calculated as the ratio of the product of the concentrations of the products raised to their stoichiometric coefficients to the product of the concentrations of the reactants raised to their stoichiometric coefficients.

A weak acid is an acid that only partially ionizes in solution, meaning it does not donate all of its hydrogen ions (H+). This is reflected in a relatively small ionization constant (Ka) value.

The ionization constant (Ka) is a measure of the strength of a weak acid. It is the equilibrium constant for the ionization of the acid in solution. A larger Ka value indicates a stronger acid, meaning it ionizes to a greater extent.

The rate law for a chemical reaction describes the relationship between the rate of the reaction and the concentrations of the reactants. It is determined experimentally and takes the form rate = k[A]^m[B]^n, where k is the rate constant, [A] and [B] are the concentrations of the reactants, and m and n are the orders of the reaction with respect to A and B.

The rate-determining step is the slowest step in a multi-step reaction mechanism. It controls the overall rate of the reaction because the other steps cannot proceed faster than the slowest step.

A catalyst is a substance that speeds up the rate of a chemical reaction without being consumed in the reaction. It does this by providing an alternative reaction pathway with lower activation energy.

The Brønsted-Lowry concept defines acids as proton (H+) donors and bases as proton acceptors. In an acid-base reaction, an acid will donate a proton to a base.

The reaction quotient (Qc) is a value that indicates the relative amounts of reactants and products present at any given time during a reaction. It can be calculated using the same formula as the equilibrium constant (Keq), but using the concentrations at any point in the reaction, not just at equilibrium.

The rate law expresses the relationship between the rate of a reaction and the concentrations of the reactants. It is determined experimentally by analyzing how the initial rate changes with varying reactant concentrations.

The order of a reaction with respect to a specific reactant is determined by the exponent in the rate law. It describes how much the rate changes when the concentration of that reactant is doubled. For example, if the rate doubles when the concentration of a reactant doubles, the order with respect to that reactant is 1 (first order).

The overall order of a reaction is the sum of the orders with respect to each reactant. It tells us how the overall rate changes when the concentrations of all reactants are doubled.

The half-life is the time taken for the concentration of a reactant to reduce to half its initial value. For a first-order reaction, the half-life is constant and independent of the initial concentration.

A unimolecular reaction involves only one molecule in the rate-determining step. For example, the decomposition of SO2Cl2 is a unimolecular reaction because the rate-determining step involves only one molecule of SO2Cl2.

A bimolecular reaction involves a collision between two molecules in the rate-determining step. In the reaction between nitrogen dioxide and carbon monoxide (NO2+CO), the reaction occurs in a single step with the two molecules colliding to form the products.

The activation energy (Ea) is the minimum amount of energy required for a reaction to occur. It is the energy barrier that must be overcome for reactants to transform into products.

The hybridization of an atom describes the mixing of atomic orbitals to form new hybrid orbitals. In sp2 hybridization, one s orbital and two p orbitals mix to form three sp2 hybrid orbitals, which are arranged in a trigonal planar geometry around the central atom. This leaves one unhybridized p orbital.

The shape of a molecule can be determined by the number of electron pairs around the central atom and the number of lone pairs. In a tetrahedral molecule, the central atom has four bonding electron pairs, arranged in a tetrahedron shape.

A seesaw shape is formed when a central atom has five electron pairs, with one lone pair. The lone pair takes up more space than the bonding pairs, causing the shape to be non-symmetrical.

A square planner molecule has a central atom with four bonding pairs arranged in a square shape. This geometry occurs when the central atom has no lone pairs, and all bonding pairs are identical.

A sigma bond is formed by the overlap of atomic orbitals along the internuclear axis. A sigma bond is single and stronger, while a pi bond results from the side-by-side overlap of p orbitals above and below the bonding axis.

Endothermic reactions absorb heat from the surroundings, increasing the enthalpy of the system, creating less disorder (lowering entropy) and thus making them non-spontaneous at lower temperatures. However, as the temperature increases, the entropy effect becomes more significant, potentially making the reaction spontaneous at higher temperatures.

Although catalysts don't change the enthalpy or entropy of a reaction, they provide an alternate pathway with a lower activation energy, speeding up the reaction rate.

The statement that states that reaction rates double when the temperature increases by 10K is incorrect. The actual rate of increase varies depending on the reaction.