HESI CHEM

Why must a chemical equation be balanced at the end of a reaction?

Because the law of conservation of mass indicates that mass cannot be created nor destroyed in a chemical reaction.

What are equilibrium reactions?

Chemical reactions that stop before all the reactants are used to make the products.

What causes equilibrium?

The state in which reactants are forming products at the same rate that products are forming reactants.

What are the four basic ways to increase the reaction rate?

Increase temperature

Increase the surface area of the reactants

Add a catalyst

Increase the concentration of the reactants.

What does increasing temperature cause in a chemical reaction?

The particles have greater kinetic energy, increasing the speed at which they move around, and the chance of collision between particles.

How does increasing the surface area of the particles in a reaction speed chemical reactions?

Gives the Particles more opportunities to come in contact with each other.

What is a catalyst?

An agent that accelerates a chemical reaction by reducing the activation energy or the amount of energy necessary for a reaction to occur.

What is the effect of increasing the concentration of reactants in a chemical reaction?

More chance collisions occur between the reactants, producing more products.

What is a solution?

A homogeneous mixture of two or more substances.

What is a solute?

The part of a solution being dissolved.

What is a solvent?

The part of a solution the solute is being dissolved in.

What are compounds?

Mixtures of different elements to create a single matter.

What are alloys?

Solid solutions of metals to make a new one. e.g. bronze ( a mixture between copper and tin)

What are Amalgams?

A specific type of alloy in which another metal is dissolved in Mercury.

What are emulsions?

Mixtures of matter that readily separate such as water and oil.

What occurs in a synthesis reaction?

Two elements combine to form a product.

What occurs in a decomposition reaction?

Breaks a compound into its component parts.

What occurs in a combustion reaction?

An exothermic (explosive) reaction occurs.

Usually initiated by heat acting on oxygen and a fuel compound such as hydrocarbon.

What are the products of the combustion of hydrocarbon?

Carbon dioxide and water.

What occurs in a single replacement chemical reaction?

An ionic compound reacts with a more active metal to create a new compound.

What occurs in a double replacement compound?

Involves two ionic compounds

The positive ion from one compound combines with the negative ion from another compound.

What is the result of a double replacement compound?

Two new ionic compounds that have "switched partners"

AB + XY \---\> AY + XB

What is chemical bonding?

The joining of an atom, element, or chemical to another.

What are the two types of chemical bonding?

Ionic and covalent

What is ionic bonding?

An electrostatic attraction between two oppositely charged ions. I.E. a cation and an anion.

Usually a metal and a nonmetal

What is covalent bonding?

When two atoms share electrons.

A single covalent bond is the sharing of one pair of electrons.

What is the strongest of any bond?

The covalent bond. Generally formed by two nonmetals.

What is a non-polar bond?

When electrons are shared equally

What are inter-molecular forces?

Weaker forces of attraction between two molecules, such as: *hydrogen bonding, dipole-dipole interactions, and dispersion forces.*

What are hydrogen bonds?

The result of the attraction for a hydrogen atom by a highly electronegative element.

Which elements are generally involved in hydrogen bonds?

Fluorine (F)

Oxygen (O2)

Nitrogen (N)

How strong are hydrogen bonds?

Hydrogen bonds are 5-10% as strong as covalent bonds, making them the strongest of the inter-molecular forces.

What are dipole-dipole interactions?

The attraction of one dipole on one molecule for the dipole of another molecule.

How is a dipole created?

When an electron pair is shared unequally in a covalent bond between two atoms or elements.

What are the charges on the ends of a dipole?

Because electrons are shared unequally, the molecule, not the covalent bond will have a positive and a negative end or side.

What are dispersion forces?

The phenomenon that occurs when electrons within an element or a compound concentrate themselves on the end of an atom.

What do dispersion forces cause?

A momentary dipole, which could be attracted to another momentary dipole of opposite charge in another element or compound.

How strong are dispersion forces?

Dispersion forces are the weakest of all the inter-molecular forces.

What is stoichiometry?

The part of chemistry dealing with the quantities and numeric relationships of the participants in a chemical reaction.

Rules for balancing chemical equations (stoichiometry)

1)Determine the correct formulas for all the reactants and products in the reaction.

2)Begin balancing with the most complicated-looking group. A polyatomic ion that appears unchanged on both sides of the equation can be counted as a single unit.

3)Save the elemental (single elements) reactants and products for last, especially if it is hydrogen or oxygen.

4)Keep your eye out for diatomic molecules such as oxygen, hydrogen, and the halogens.

5)If you get stuck, double the most complicated-looking group and try again.

6)Finally, make sure that all coefficients are in the lowest possible ratio.

7)No fractions! Don't mess with subscripts.

What is the function of the coefficients in a chemical reaction?

Coefficients are put in front of chemical compounds and used in a ratio to compare how much of one substance is needed to react with another in a certain reaction.

What do oxidation/reduction reactions involve?

The transfer of electrons from one element to the next

What is oxidation?

Loss of electrons

What is reduction?

Gain of electrons

Why is the oxidant reduced?

Because it loses an electron

How is the element being oxidized and the element being reduced identified?

Determining the oxidation states of all elements in the compound.

What are the rules to determine oxidation states?

Element by itself\=0

Group 1A\= always +1

Group 2A\= always +2

Halogens\= +1 *positive with Oxygen*

Monatomic Ion\= Ion charge

H\= +1 with nonmetals

-1 with metals

O\= Usually -2, -1 with peroxide *(H2O2)*

F\= Always -1

Sum of ON (oxidation \#) for a neutral compound \= 0

Sum of ON for a polyatomic ion \= ion charge

Group 1a of the periodic table includes

hydrogen (H), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

*Highly Nasty Kids Rub Cats Fur*

Group 2a of periodic table includes

beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

The halogens include

fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At)

*Note-see special rule for Fluorine*

What are exceptions to the elemental oxidation rule?

O2

H2

Br2

N2

I2

F2

What is the effect of acids on metals?

Acids are corrosive to metals.

What color do acids take when in contact with blue Litmus paper?

Red

What occurs to acids when mixed with bases?

Become less acidic

What are bases?

Substances that denature proteins, making them feel slick.

What color do bases change red Litmus paper to when in contact?

Blue

What occurs to bases when in contact with acids?

They become less basic.

What are acids?

Compounds that are hydrogen or proton donors

What is hydrogen in its ionic state?

A proton

What is hydronium?

A water molecule plus a proton (hydrogen)

What group do bases generally have as a makeup of its molecule?

Hydroxide (OH) group

What is the concentration of acids expressed as?

pH

What does the pH scale measure?

Alkalinity or acidity.