Unit 4 Lesson 6

Types of Reactions

Combination - A + B ---> AB

• several reactants combine into a single product

Decomposition - AB ---> A + B

• compound breaking down

Single Exchange - A + BC ---> AC + B

• Compound breaks apart with 1 part combining with the other reactant

Double Exchange - AB + CD ---> AD + CB

• Both reactants break apart and recombine

Practice Problems
6) Li(s) + 2HCl2(aq) ---> H2(g) + LiCl4(aq)
7) AgNO3(aq) + NaOH(aq) ---> NaNO3(aq) + AgOH(s)

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Unit 4 Lesson 5

Atom Inventory

Balancing Chemical Equations

Balanced chemical equations show the true mathematical relationship between the reactants and the products in a chemical reaction.

• When balancing, start with atoms that only show up once on each side of the equation
• You can only change the coefficients
• Coefficients indicate how many "units" of an element or compound are present

Ex: __N2(g) + __H2(g) ---> __NH3(g) this equation is unbalanced because there are 2 nitrogen atoms and 2 hydrogen atoms in the reactant side but there is only 1 nitrogen and 3 hydrogen in the product. To fix this, change the coefficients.
N2 + 3H2 ---> 2NH3 Now this equation is balanced because there are 2 nitrogen atoms on both sides and 6 hydrogen atoms on either side.
Practice Problems

3) a. Make three loaves of bread because 6 divided by 2 is 3
    b. because if you multiply all the ingredients by 3 it's balancing both sides of the recipe to use all six bananas.

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Unit 4 Lesson 4

Conservation of Mass

• Can't create or destroy matter
• Mass (# of atoms) and weight (force of gravity) are different
• Gases have mass

If one of the products of a chemical reaction is a gas, the mass of the products will be less than the mass of the reactants, unless you trap the gas.

Mass Change

• Individual atoms are conserved in chemical reactions and physical changes. The number of atoms of each element remains the same from start to finish.
• Mass is conserved in chemical reactions. The total mass of the products equals the total mass of the reactants.

Practice Problems
4) when an ice cube melts, what quantity changes? C- its volume
7) trap the gas and ash left and weigh it.

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Unit 4 Lesson 3

Physical Vs. Chemical Change

Physical Change - change in matter in which a substance changes form but not identity. These can also include color or temp.

• Ex: H2O(l) ---> H2O(s)

Chemical Change - change in matter resulting in the formation of a new substance or substances with new properties.

• Ex: 2Na(s) + Cl2(g) ---> 2NaCl(s)

You're not always able to see if a physical change is accompanied by a chemical change simply through observation. You need a chemical equation.

Dissolving of a substance can either be physical or chemical but is considered physical.

Practice Problems
1) physical change is not a change in identity of the substance while a chemical change is a change in identity by rearranging the atoms.
6) a. Chemical because the product is not identical to the reactants b. Physical because only the phase of the substance changes

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Unit 4 Lesson 2

Making Predictions

Observing Change

When a substance changes phase or dissolves, its chemical formula does not change.

When you look at a chemical equation, it can tell you the different kinds of changes going on like changes in phase or identity of the substance.

Ex: CaCl2(aq)+ 2NaOH(aq) ---> Ca(OH)(s) + 2NaCl(aq)

For this chemical equation you start of with two aqueous reactants, but when they undergo the reaction you can tell that there was a change visually because now one of the products is a solid that you would be able to see. The equation would also allow you to see which substances broke up and rearranged to combine into a solid. You wouldn't be able to know this without seeing the chemical equation.

Some things a chemical equation alone can't tell you is if there were any changes in temperature or color after or during the reaction or how quickly it happened.

Practice Problems

4) a. NaCl(s) ---> NaCl(aq) b. MgS(s) ---> Mg(s) + S(g) c. Ti(s) + O2(g) ---> TiO2(g)

5) a. Two aqueous solutions combining leaving behind water and emitting chloramine gas and aqueous sodium hydroxide b. two aqueous solutions combining to produce hydrazine gas, aqueous sodium chloride, and water

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Unit 4 Lesson 1

Toxic Reactions

Chemical Equations

Chemical formulas

• Represent changes in matter using symbols and formulas.
• Describe what happens when a single substance is changed or two or more are combined causing a change.
• Substances that you start with are called reactants and when the change takes place you end up with products.

Ex Chemical Equation: NaCN(s) + HCl(aq) ---> NaCl(aq) + HCN(g)The interpretation of a chemical equation is telling you exactly what is happening in the reaction.

The interpretation of the equation above(colors correspond): Solid sodium cyanide reacts with hydrochloric acid to produce aqueous sodium chloride and gaseous hydrogen cyanide.

Some chemicals react negatively to substances in the body and are called toxins.

Toxins - substances that interact with living organisms and cause harm.

Toxins Enter the Body

• React with water in body
• Could be molecular, ionic, or metallic substances

Practice Problems
3) a toxic substance is something that enters the body and then reacts with substances in the body where the products are harmful.
6) Forming solids that clog places in the body. Bad metals compete with good metals that the body needs. Acidic products that damage tissue.

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Unit 3 Summary

Unit 3 was all about how gas pressure, density, temperature, and the number of molecules all relate to one another to give make up the gas laws. These gas laws have significant importance to weather patterns and formation.

Gas Laws

Charles's Law: k=V/T constant k = volume/temperature

Boyle's Law: k=PV constant k = pressure x volume

Gay-Lussac's Law: P=kT pressure = constant k x temperature

Combined Gas Law: k=PV/T constant k = (pressure x volume)/temperature

Ideal Gas Law: PV=nRT (pressure x volume = (number of moles/molecules) x (constant R 0.082) x (temperature)

• For all the gas laws, the temperature has to be in degrees Kelvin

A lot of the weather we experience has to do with phase changes water goes through

• Evaporation- the phase change from liquid to gas
• Condensation- the phase change from gas to liquid
• Freezing- the phase change from liquid to solid

Density is a recurring factor in all aspects of weather including:

• humidity which is the water density in the air
• pressure because the more dense the number of molecules in the air, the higher the pressure
• The warmer the air is the higher the water density can be and exceeding that maximum results in precipitation

Practice Problems

 

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Lesson 19

Hurricanes

• Destructive storms characterized by strong winds and rainfall
• Tropical Depressions---> tropical storms---> hurricanes

5 categories determined by strength for hurricanes are from 1-5 --> least-most intense

Tropical storms - a lot of warm water evaporates

• Moves over warm water and evaporation increases

Water vapor density is related to temperature

As temperature increases, so does the water vapor density.

This means that colder temperatures have a lower maximum density where the density is 100%

 

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Lesson 18

Humidity and Condensation

Humidity - density of water vapor in the air; dependent on temperature and pressure

• measure of the amount of water vapor in the air
• Temperature that water condenses indicates how much water vapor is in the air

When the temperature is colder then the water vapor in the air is less dense and as the temperature rises, the density increases.

Relative Humidity - amount of water vapor in the air compared to water vapor possible for a specific temperature; indicated as a percent

• Upper limit to amount of water vapor that is possible at a given temperature

Practice Problems

5) 2.2 mol/1000 L

7) 1.6/4 = .4 mol/1000 L

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Lesson 17

Ideal Gas Law

• Relates temperature, pressure, volume, and number of moles of particles
• Formula: PV=nRT
• R is the constant and R = 0.082 • atm/mol • K
• R is the same for all gases
• R can change with different units like changing Liters to Milliliters

To find the total number of molecules in a sample of gas, take the number of moles and multiply by (6.022 • 10^23)

Practice Problems

1) the ideal gas law is: pressure x volume = number of molecules or moles x the constant 0.082 x temperature

 

2)

 

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Lesson 16

Avogadro's Law

To count the number of molecules in a specific volume of gas, the unit is counted in moles.

• 1 mole = 6.022 x 10^23 (also called Avogadro's number)
• 1 mole at standard temperature of 273°K and standard pressure of 1 atm occupies a volume of 22.4 L
• This standard temperature and pressure is abbreviated STP

Avogadro's Law - If two gases have the same pressure, volume, and temperature, then they have the same number of gas molecules independent of the identity of the gases.

Practice Problem

5) 8.0 g of helium has more atoms because 8g is two atoms and 40g of argon is only one argon atom.

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Lesson 15

Pressure and Number Density

The number of molecules in a gas is directly related to the pressure.

When the gas pressure increases, this means that there was an increase in the number of gas molecules per unit of volume.

• Number of gas molecules is represented by the letter n.

Formula: P=k(n/V)
Number Density- the number of gas particles per unit of volume which can be found by dividing the number of molecules by the volume - n/V

You can determine the pressure by measuring the difference in height of a liquid.

Practice Problems

1) decrease in air pressure with increasing altitude comes from the fact that the number density of molecules in the air decreases with the rises in altitude, ultimately lowering the gas pressure. 

6) a. B has the least air pressure because even though it has the same numbe of molecules as A, it's volume is larger making it less pressure per liter. 

A has the next largest pressure because even though it's volume is the same as C, there are fewer molecules, giving it a lower number density. 

C has the largest gas pressure because it is the small volume with the most molecules, giving it the highest number density, so a higher pressure. 

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Lesson 14

High and Low Air Pressure

Clouds are just water droplets suspended in the air and to form there needs to be moisture in the air

Formed from:

• Conditions of low temperature and pressure
• In warm air mass- the water vapor in the air rises and cools off
• Change in pressure
• Changing phase from vapor to droplets

Clouds under go changes in pressure and temperature but the volume stays the same

-as pressure increases, the temperature also increases

Warm air rises

Low Pressure:

• Associated with fronts, storms, clouds, and precipitation
• Warm and cold air meets and the warm air rises which leaves behind low pressure (since there is low temp.)
• This low temperature brings cloudy and rainy weather

High Pressure:

• Clear skies
• Denser air is sinking, inhibiting rain and clouds

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Lesson 13

Combined Gas Law

When all three variables of temperature, pressure, and volume are variables and none stay constant, you need to use the Combined Gas Law.

Formula

• k=(P)(V)/ T - the proportionality constant k equals the original pressure multiplied by the original volume all divided by the original temperature.
• After finding this proportionality constant, you can plug it into the equation along with the rest of your changed values to find either the new pressure, volume, or temperature.

Changing gas pressure has more of an effect on volume than results that may have come from changing the temperatures.

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Lesson 12

Molecular View of Pressure

Gas pressure is caused by the movement and collision of molecules

• Collision of molecules into the container only
• Increase in temperature causes an increase in pressure because the molecules hit the container faster and with more force
• Decrease in volume causes an increase in pressure because the molecules are forced into a smaller space and hit the container more often

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Lesson 11

Gay-Lussac's Law

- pressure of a given amount of gas is directly proportional to the temperature if the gas volume and amount of gas do not change and if the temp. is expressed in degrees Kelvin.

Changing pressure can depend on the type of container the gas is in:

Flexible Container- changing temperature or pressure changes volume of gas.

-This comes from the container allowing the gas to expand the container walls out

Rigid Container- increasing temperature causes pressure to increase

- since the container won't allow the gas volume to expand, it can't relieve some of the pressure so the pressure rises along with the temperature.

Formula

• k=P/T - constant k equals the original pressure divided by the original temperature
• V is missing from the equation because the volume is not changing

 

 

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Lesson 10

Boyle's Law

In Boyle's Law the relationship between gas pressure and gas volume are inversely proportional meaning that instead of one increasing, causing the other to increase, when one increases then the other decreases.

inverse proportion - two variables are inversely proportional to each other if one variable increases when the other decreases.

Formula

• k=PV
• k is the proportional constant that you find by multiplying the original pressure and volume
• You then solve either for the new pressure or the new volume by plugging in the k value
• The term missing from this equation is the temp. Meaning that it is the term that stays the same while pressure and volume change

 

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Lesson 9

Air Pressure

-force per unit area exerted on objects as a result of gas molecules colliding with those objects

Pressure - force applied over a specific area

- gas pressure caused by gas molecules striking objects or the walls of a container

Two Types

• Air pressure trapped inside a container
• Air pressure from the atmosphere outside

- atmosphere: mixture of gases surrounding you

- atmospheric pressure: air pressure that's always present on earth as a result of air molecules colliding with the surfaces of objects

Sea level has 14.7 lb/in squared of air pressure or 1 atm.

Practice Problems

3) the balloon would instantly expand until it popped because of the lack of outside air pressure

5) the cabin pressure and the pressure inside your head is a lot more than the air pressure outside the plane.

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Lesson 8

Gas Density

Water exists in many forms

• Vapor
• Fog
• Clouds
• Liquid water

Sublimation - the phase change from solid directly to gasEvaporation - phase change from liquid to gas

Molecules of a gas are 1,000 times more dispersed than solids

When you are calculating the density of a substance by using the formula for density, there is a way to check your how close you were to the actual value. This is called your percent of error.

-first find your value then subtract the accepted (or actual) valuefrom your value

-next divide that answer by the accepted value and then convert to percent and you have your percent of error

Practice Problems

1) gas is not as dense as a solid. That's why objects can pass through a gas

3) sublimation is the process of the phase change from a solid directly to a gas and evaporation is the phase change of a liquid into a gas.

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