Hemet High  Chemistry Name:Pd:

Chapter 18/21 Homework Packet

Date Assigned / Date Due / Assignment / Stamp
All Chapter 18/21 Notes Completed / _____/10pts
18.2 Worksheet
18.1 Worksheet
Ch 21.1 pg 703 #11-13
Half-Life Worksheet
Ch 18/21 Review Worksheet
Final Packet / ___/60

Test is on

Hemet High  Chemistry

18  Chemical Equilibrium

Chapter Notes

Section 18.2 - Shifting Equilibrium

Reversible Reactions

______: one in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously.

The ______arrow tells you that the reaction is reversible.

2 SO2(g) + O2(g) ⇄ 2 SO3(g)

______: when the rates of the forward and reverse reactions are equal, the reaction has a reached a state of balance.

At chemical equilibrium, ____ net change occurs in the ______amounts of the components of the system.

The relative concentrations of the reactants and products at equilibrium constitute the ______of a reaction.

Think of a 2-story mall with an escalator. You have 100 people on the top floor and 50 people on the bottom floor. If 10 people want to move to the top floor, how can this happen while still keeping 100 people on the top and 50 people on the bottom?

Factors Affecting Equilibrium: Le Châtelier’s Principle

Le Châtelier’s Principle: If a ______is applied to a system in dynamic equilibrium, the system changes in a way that ______the stress.

There are three factors that we will talk about that can affect equilibrium.

CONCENTRATION

If you add more of a ______, the reaction goes toward the ______.

If you take away some of a ______, the reaction goes toward the ______.

If you add more of a ______, the reaction goes toward the ______.

If you take away some of a ______, the reaction goes toward the ______.

TEMPERATURE

If heat is a ______and you add heat, the reaction shifts toward the ______.

If heat is a ______and you add heat, the reaction shifts toward the ______.

If heat is a ______and you take away heat, the reaction shifts toward the ______.

If heat is a ______and you take away heat, the reaction shifts toward the ______.

PRESSURE – ONLY GASES!!

If you ______pressure, the reaction shifts towards the side with _____ moles.

If you ______pressure, the reaction shifts towards the side with _____ moles.

VOLUME – ONLY GASES!!

If you ______volume, it is the same as ______pressure, so the reaction shifts towards the side with ______moles.

If you ______volume, it is the same as ______pressure, so the reaction shifts towards the side with ______moles.

Because it is the same as changing pressure, we ______consider this to be a 4th factor.

CATALYSTS

Adding a catalyst has no effect on the equilibrium, it will only help to reach equilibrium faster.

Reactions to Completion

A reaction is considered to “go to completion”, when almost all of the _____ are removed from the solution.

This depends on the ______of the product formed, and if it is ______, then on its degree of ______.

Formation of a Gas

Gases are not very ______, so when a gas is formed and the reaction container is ______to the air, the gas will escape and the reaction will go ______to completion.

Formation of a Precipitate

If a product is ______(a precipitate), then when the product forms, it ______dissolve to allow the reaction to go in the reverse direction.

Formation of a Slightly Ionized Product

This occurs with the neutralization reactions of ______and ______.

HCl(aq) + NaOH(aq)

Water only slightly ionizes, so it exists as mainly ______molecules.

Section 18.1 - The Nature of Chemical Equilibrium

Equilibrium Expressions

______: Keq is the ratio of product concentrations to reactant concentrations at equilibrium.

nA + mB ⇄ xC + yD

Keq = [C]x [D]y*Remember: it is

[A]n [B]mproducts over reactants!

Write Equilibrium Expressions:

H2 + I2↔ 2HI

2HgO ↔ 2Hg + O2

2SO2 + O2↔ 2SO3

N2 + 3H2↔ 2NH3

Equilibrium Constants

To find an Equilibrium Constant (Keq), plug in the ______of the reactants and products into the equilibrium expression and solve!

Keq> 1, ______favored at equilibrium

Keq < 1, ______favored at equilibrium

Keq does not have any units!

Calculating Keq

A liter of a gas mixture at equilibrium at 10°C contains 0.0045 mol of N2O4 and 0.030 mol of NO2. Write the expression for the equilibrium constant and calculate Keq.

N2O4(g) ⇄ 2NO2(g)

An equilibrium mixture of N2, O2, and NO gases is determined to consist of 6.4 mol/L of N2,

1.7 mol/L of O2, and 1.1 mol/L of NO. What is the Keqfor this system?

N2 + O2⇄ 2NO

Hemet High  Chemistry

21Nuclear Chemistry

Chapter Notes

Section 21.1 – Radioactivity

•Wilhelm Roentgen made a big discovery in 1895. He found that invisible rays were emitted when electrons bombarded materials. He named these rays, .

•At the same time, Henri Becquerel was studying minerals that emitted light after being exposed to sunlight, a phenomenon called phosphorescence.

• and her husband Pierre were working with Becquerel and took his mineral sample and were able to isolate the components emitting the rays.

•Marie named the process by which materials give off such rays .

• : the penetrating rays and particles emitted by a radioactive source.

•Marie Curie was the first to win the Nobel Prize and is the only person to receive Nobel Prizes in two different sciences--physics and chemistry!

Nuclear Reactions vs. Normal Chemical Changes

•Marie Curie discovered that:

•Nuclear Reactions involve the , which changes the type of element.

•Chemical reactions involve , not protons and neutrons.

•When a substance emits , it changes its identity.

•A element has an unstable nucleus.

•Isotopes are atoms of the same element that have

• :isotopes of atoms with unstable nuclei

Types of Radiation

•The three types of nuclear radiation are radiation, radiation, and radiation.

• There is also and they can be separated by an electric field.

Alpha Decay Radiation

• : a positively charged helium isotope.

•Written with the following symbol:

•It contains 2 protons and 2 neutrons and has a 2+ charge

Beta Decay Radiation or Electron Capture

• : a very fast moving electron, resulting from the breaking apart of a neutron.

•Written with the following symbols:

Positron Emission Radiation

  • : a particle with the same mass as an electron, but has a positive charge.
  • Emitted from the nucleus during some kinds of radioactive decay. Symbol:

Gamma Emission Radiation

• : high energy electromagnetic radiation.

•The emission of gamma rays the atomic number or mass number of a nucleus.

•Written with the following symbol:

EXAMPLES:

Write the nuclear reaction for the following:

Alpha Decay – Symbol:

Beta Decay – Symbol:

Electron Capture – Symbol:

Positron Emission – Symbol:

Gamma Emission

1.


Section 21.2 - Penetrating Abilities and Half-Life

Penetrating Abilities

• : stopped by piece of paper.

• : stopped by thin metal

• : stopped by thick lead and concrete.

Half-Life

• : the time required for one-half of the nuclei of a radioisotope sample to decay to products.

•After each half-life, of the existing radioactive atoms have decayed into atoms of a element.

Half-Life Calculation

•Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 2040 g of Carbon-14. How long is three half-lives and how many grams of the isotope remain at the end of three half-lives?

The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be left after 9.6 minutes has elapsed?

  • Os-182 has a half-life of 21.5 hours. How many grams of a 10.0 gram sample would have decayed after exactly two half-lives?