SAAT Chemistry Section 4 (Thermochemistry and Chemical Calculations) - تحصيلي

Energy

The ability to do work or produce heat

Chemical potential energy

The energy stored within the structural arrangement of atoms and molecules, specifically held within chemical bonds

Heat

The energy that is in the process of flowing from a warmer object to a cooler object (represented by q)

Calorie(Cal)

The amount of energy required to raise the temperature of one gram of pure water by one degree celsius

Calorie formula

Cal = 1000 cal = K cal

Specific heat

The amount of heat energy required to raise the temperature of one unit mass (typically 1 kilogram or 1 gram) of a substance by one degree celsius

Calculating heat formula

q = c x m x △T

Calorimeters

A scientific instrument used to measure the heat of chemical reactions or physical changes, as well as heat capacity

Enthalpy (H)

The heat content of a system at constant pressure

Enthalpy formula

△Hrxn = H_final - H_initial

When the △H rxn is positive, the reaction is said to be

Endothermic and is written in the reactants

When the reaction is negative, the reaction is said to be

Exothermic and is written in the products

Thermochemical equation

Balanced chemical equation that includes the physical states of all reactants and products and the energy change, usually expressed in △H (enthalpy)

Molar enthalpy (heat) of vaporization (△Hv)

The heat required to vaporize one mole of a liquid

Hess’s law

States that if you can add two or more thermochemical equations to product a final equation for a reaction, then the sum of the enthalpy changes for the individual reactions is the enthalpy change for the final reaction

Standard enthalpy (heat) of the formation

Of one mole of the compound in its standard state from its elements in their standard states

Balanced chemical equation

A statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction

Coefficient

The number written in front of a reactant or product; usually whole numbers and are not usually written if the value is one

Subscript (s)

Solid

l

Liquid

g

Gas

aq

Aqueous

Balanced equations reflects

Mass and charge balances

Chemical reaction

The process by which the atoms of one or more substances are rearranged to form different substances

Equations

Show a reaction’s reactants, which are the starting substances, and the products, which are the substances formed during the reaction

Synthesis reaction

Chemical reaction in which two or more substances (A and B) react to product a single product (AB)

Decomposition reaction

When a single compound breaks down into two or more elements or new compounds

Replacement reaction

It divides into single (simple) and double displacement

Single substitution

A reaction which the atoms of one element replace the atoms of another less reactive element in a compound

Double substitution

Involves an exchange of ions between two compounds

Combustion reaction

Oxygen combines with a substance and releases energy in the form of heat and light

Mole

An amount of matter; an amount of substance that contains Avogadro’s number of particles

Mole of an element

Its relative atomic mass in grams

Mole of a compound

Its relative molecular mass in grams

Avogadro’s constant

The number of individual particles in one mole of any substance

6.022 × 10²³

Molar volume

The volume of one mole of any gas is 24 dm3 at r.t.p regardless of the identity of the gas

Mole ratio

Chemical substances react with each other in moles

Solutions

Made when solutes dissolve in solvents

How solutions are discribed

By their concentration

Concentration

It’s the number of moles of the solute in certain volume of the solution

Empirical formula

The simplest whole number ratio of the atoms in a compound

To calcular the empirical formula

Write masses/percentage of each element

Divide the massby its molar mass to find the number of moles

Divide by the smallest number

Multiply by the whole number

Molecular formula

The actual number and type of atoms in one unit of compound

Percentage composition by mass

Percent of an element in a compound = (mass of the element/mass of the compound)(100)

Purity

Mass of pure substance/mass impure (actual substance)

Limitng reagent

The reactant that determines the amounts of the actual producal products

Percentage yield

The percentage between what we calculate (theoretical) and what we really get (actual)

Percent yield formula

(actual yield/theoretical yield)(100)