Unit 4, Lessons 5 and 6

Lesson 5:

For a chemical equation to demonstrate a chemical reaction that's actually possible, it must represent a true mathematical relationship between products and reactants. Simply put, there must be an equal number of atoms on each side of the equation. This ties into the law of conservation of mass and that of matter. "True mathematical relationship" is synonymous with "balanced." You can balance an equation by adding coefficients, and coefficients only. Not the little numbers at the bottom, subscripts. Coefficients let scientists know how many molecules or single atoms of a substance there are in an equation. They're measuring tools!

Problems:

1.) Why do chemical equations need to be balanced? Chemical equations that aren't balanced make for reactions that either don't work properly or don't happen at all. When they are balanced, the reactions are easier to control, and typically give one their desired result!

2.) How are subscripts and coefficients different from one another in chemical equations? If there is a substance with an atom that has a subscript, that tiny number only applies to the element that it hugs. The coefficients, however, must be distributed, and thus multiply everything in a compound.

Lesson 6:

Chemical reactions can be classified to a degree further than just "chemical" or "physical". When one looks at a chemical equation, they might notice that some elements or molecules switch places in the products. The new types of classification we learned in Lesson 6 are as follows:

Combination: A + B --> AB

Single exchange: A + BC --> AC +B

Double exchange: AB + CD --> AD + CB

Decomposition: AB --> A + B

In combination reactions, reactants combine and form one single product.

In single exchange reactions, reactants combine and one factor from either the first compound or the second switches to create two different products.

In double exchange reactions, two factors, one from both compounds, switch places and make two different products.

In decomposition reactions, an already existing substance breaks apart into its components.

Problems: 

4.) List four molecules and four ionic compounds from the reactions in exercise 3.

                    MOLECULES                                     IONIC COMPOUNDS

                           HNO3(aq)                                                       MgBr2(s)

                             Cl2(g)                                                            NaOH(aq)

                           C2H4(g)                                                          NaNO3(aq)

                              Br2(s)                                                           MgCl2(s)

6.) Solid lithium reacts with aqueous hydrochloric acid to produce hydrogen gas and aqueous lithium chloride: 2Li(s) + 2HCl(aq) --> H2(g) + 2LiCl

^ There are 2 lithium atoms, 2 hydrogen atoms, and 2 chlorine atoms on both sides

Unit 4, Lessons 3 and 4

Lesson 3:

Although the interactions between substances are considered chemical reactions, the changes that the substances go through can be either physical or chemical. A physical change implies that the products (what happens after two or more factors are combined) can be altered in order to regain the reactants. A bowl of trail mix is a good example; you can throw together some pretzels, some cracker chips, some raisins (but who likes raisins in their trail mix anyway?), and some M&Ms in a bowl and then pick out each individual food afterward. A chemical change, on the other hand, can't be so easily reversed. If you mix together eggs, oil, cake mix, and throw that sucker in the oven, you most certainly won't get eggs, oil, and cake mix when you take it out. All the ingredients combine to form a new substance with new (and in this case, delicious) properties.

Problems:

2.) Explain how dissolving can be described as either a physical change or a chemical change. Dissolving is a physical change because a solid changes forms and seems to disappear in a liquid. The liquid can be boiled and the solid will be left behind, such as in the case of salt water. However, also using salt water as an example, sodium and chlorine atoms break apart in water and conduct electricity. Technically, this is the product, which has new properties. Solid salt doesn't conduct electricity.

6.) Classify the following two changes as physical or chemical. Explain your reasoning.
A.) CaCO3(s) + H2SO4(aq) --> CaSO4(aq) + CO2(g) + H20(l) Chemical change, because the products are both different substances and in different phases than the reactants.
B.) NaCl(s) --> NaCl(l) This is just a physical change. The product still has its identity; it is still salt, but it's in liquid form. Now it's salt water.

Lesson 4:

The law of conservation of mass states that, in a chemical reaction, or any action for that matter, mass cannot be created or destroyed. It can, however, go somewhere else. In a chemical equation, the mass of the products is the same as the reactants, even if one of the products is a gas, unless the gas is trapped in a sealed-off container. The mass does not change, regardless of the phase change or the factors being combined, because all atoms are accounted for.

Problems:

2.) Explain how the law of conservation of mass applies to garbage. The law of conservation of mass applies to garbage in that garbage sits in landfills for years, and only some of it biodegrades. What doesn't biodegrade still has matter--and mass, because it exists. We recycle that garbage by taking it and making it into usable products, like bottles, recycled paper, whatever have you. The mass of the garbage is not lost, but it changes forms.

7.) What would you have to do to prove that matter is conserved when a piece of paper is burned? The paper would have to be burned in sealed-off container, such as a glass box or something of that sort. That way, once the paper is burned, both its ashes and any gas released from the burning process is still present. Just find out the mass of the box with a scale.

Unit 4, Lessons 1 and 2

Lesson 1:

A chemical equation illustrates what happens, and what substances are involved, in chemical reactions. They are a way that scientists keep track of matter. Most chemical equations write out the substances involved in a reaction in the same way that mathematicians do. One one side of the equation, two reactants are added together, and on the other side, addition is also used. A further example is:

2HCl(aq) + Cr(s) --> CrCl2(aq) + H2(g)

Which is read aloud as:

"An aqueous solution of hydrochloric acid reacts with solid chromium to produce an aqueous chromium chloride solution and hydrogen gas."

Not everything about a chemical reaction can be observed through the senses, which is why these equations exist! Two substances, like hydrochloric acid and water, water and salt water, things like that...can all be clear, and therefore we might not be able to tell the difference between them. 

Problems:

1.) What is the difference between  reactant and a product? A reactant is what is combined with another substance (another reactant) in a chemical equation. The product is what the reactants make, and usually marks the end of the reaction.

6.) Describe at least three types of effects that a toxic substance can have on the body. If ingested, a toxin can cause severe nausea, diarrhea, blood acidosis, or possibly even kidney stones. If taken in through the nose, perhaps even the skin, hallucinations can occur.

Lesson 2:

In addition to specifying which substances are what, chemical equations also clue us in to possible phase changes. From them, we can predict what we might observe during a reaction. For example, the equation in Lesson 1 tells us that an aqueous solution and a solid come together to create a liquid with a solid precipitate (another aqueous solution) and a gas. There will probably be some bubbling, some evaporation, to produce the hydrogen. If we have bubbles rising, we might need some heat, so a temperature change could also be observed.

Problems:

2.) Use chemical equations to describe the difference between sugar melting and sugar decomposing. The formula for sugar is C12H22O11. The melting process of sugar is a physical change, because sugar molecules don't have to change their identity. The chemical equation or melting sugar is C12H22O11(s) --> C12H22O11(l), and vice versa as sugar sets afterwards. Decomposing sugar, however, involves the splitting of sugar molecules. They break apart, as the word suggests. The chemical equation for decomposing sugar is C12H22O11(s) --> 12C(s) + 11H20(g).

4. Write a chemical equation for these reaction descriptions:

A.) Solid sodium chloride dissolves in water. NaCl(s) + H2O(l) --> NaCl(aq)

B.) Solid magnesium sulfide is heated to produce solid magnesium and sulfur gas. MgS(s) --> Mg(s) + S(g)

C.) Solid titanium is heated in oxygen gas to produce titanium dioxide. Ti(s) + O2(g) --> TiO2(s)

Unit 3, Lesson 19

Hurricanes form in stages, the first being a tropical depression, which is simply an area of low pressure that has the potential to produce heavy precipitation. The tropical depression has the power as it makes its way toward land to develop into a tropical storm, which is a phenomenon that can drop lots of rain with lots of wind. At the hurricane stage, rain causes flooding and winds become so violent that homes can be destroyed, sometimes even leveled. The eye of a hurricane, which has been speculated to be the safest place in the storm, is a core of cold air around which clouds spin continuously. The spinning, and winds around the storm, push it in different directions.

Problems:

1.) What conditions are necessary for hurricane formation? For a hurricane to form, the following conditions must be present: low air pressure, winds of or above 75 mph, moist, warm air rising from the ocean, and cloud formation high in the sky in a spiral pattern.

Unit 3, Lessons 17 and 18

Lesson 17:

This unit tacked on another gas law to the three we've already learned about. It's called the ideal gas law, and it's described by this formula!:

PV = nRT

Check my summary for lesson 16 to remember what the letters stand for. This equation is helpful in finding almost anything you need and is closely associated with STP: standard temperature and pressure. Typically we use the ideal gas law to find out the volume or or the number of moles present in a sample of gas.

Problems:

3.) How many moles of hydrogen, H2, gas are contained in a volume of 2 L at 280 K and 1.5 atm?

PV = nRT

(1.5)(2) = n(0.082)(280)

3 = n(22.96)

n = 0.13 mol, there are 0.13 moles of hydrogen in his sample.

Lesson 18:

Humidity is defined as the amount of water present in an air (see: Florida). Humidity increases or decreases by evaporating from a larger body of water or by condensing onto a solid object, such as a glass of ice water (why glasses of tea "sweat"). The total number of moisture in the air is called relative humidity and cannot exceed 100%, but can be determined by finding the difference between the readings on a dry-bulb and wet-bulb thermometer. Warm air can hold more water than cold air, which explains why clouds form on cold days.

Problems:

1.) What does humidity measure? The amount of water present in the air.

Unit 3, Lessons 15 and 16

Lesson 15:

A plane in flight gains elevation after lifting off the runway. Passengers in the plane's pressurized cabin don't feel the change, but outside the plane, the pressure and temperature of the air decreases and breathing becomes difficult. There aren't as many molecules at high elevations to support life or respiration, so gases are lighter and, ultimately, colder. Hence, the relationship between altitude, pressure, and density. The number of molecules, however many there may be, can be described by the term number density, which is represented by the following formula:

n/V

where n is the number of moles--a fancy term used to describe how many atoms there are in a sample of gas. 

Problems:

2.) Use the kinetic theory of gases to explain the relationship between number density and gas pressure. As I stated in my summary of this lesson, as pressure increases, there are more molecules condensed into a space, and vice versa. If the pressure drops, there are less molecules. The molecules don't change the speed at which they fly, but there are less of them, which means they don't bump into one another/change direction as often.

Lesson 16:

Our friend the mole is represented by the number 6.022x10^23, or 602 sextrillion--huge! Moles are measurements of how many atoms, particles, whatever-you-want-to-call-them there are in a sample of gas. If you don't know how many moles are present, use this nifty equation to figure it out:

PV = nRT

where P = pressure, V = volume, n = moles, R = the constant (0.082) for all gases, and T = tempterature (in  Kelvin.) Though any value can be plugged in for those variables to find another, it's more common to see the equation used at STP, the standard temperature and pressure, which are 273 K and 1.0 atm.

Problems:

5.) Which has more atoms: 8.0 g of helium, He, or 40.0 g of argon, Ar? Explain. Both of these elements are noble gases, but argon is in a larger quantity, so I'd say 40.0 g of Ar has more atoms.

7.) At 25 degrees C, which balloon has the greater volume: an oxygen, O2, balloon at 1.2 atm with a mass of 16.0 g, or a helium, He, balloon at 1.2 atm with a mass of 2.0 g? By Avogadro's law, two samples of gas at the same temperature and pressure are said to have the same number of particles regardless of their mass. This, in turn, should make their volumes the same. The two balloons have an equal volume, but you'll need 8x as more He to equal O.

Unit 3, Lessons 13 and 14

Lesson 13:

Sometimes all the variables in your sample of gas change. Say that your pressure increased or decreased, making for a rise or drop in temperature, and that influenced the sample's volume. What ever would you do to find that one missing piece? You'd use the Combined Gas Law, of course, which is as follows:

k = P(V) / T

Typically, we see this formula being used to solve equations like what I've described; the need to find a volume. It can also be called for in altitude problems, where say a balloon has risen to a higher altitude than sea-level and the pressure has changed.

Problems:

(WILL BE ADDED LATER)

Lesson 14:

We've already found out that warm and cold fronts are associated with different kinds of weather, but whether you have a sunny day or a rainy day is also dependent upon what the air pressure is. Areas of low pressure are, as you could probably guess, associated with colder temperatures and more snow/rain. This happens because the cold air means that particles move slower, which allows for condensation, then clouds, and eventually precip. High pressure areas are warmer, sunnier, and more pleasant. When high and low pressure areas meet, the high pressure air rises above the denser cold pressure air.

Problems:
(WILL BE ADDED LATER)

Unit 3, Lessons 11 and 12

Lesson 11:

Gay-Lussac's law tells us that the pressure of a given amount of gas is proportional to its temperature and that the volume of that sample will never change. Temperature, usually expressed in Kelvin, plays a role in this equation:

k = P/T

where k is the proportionality constant, as it was in Boyle's law. A simpler way to describe this law, and if you could picture it on a graph you'd see why, is to say that as temperature rises, the pressure increases, and while the pressure decreases, the temperature drops as well.

Problems:

(WILL BE ADDED LATER)

Lesson 12:

This lesson was relatively self-explanatory. The kinetic outlook on gases tells us that gas molecules are already in motion--which we knew. We can take this outlook and apply it easily. The more pressure you put on a sample of gas, the more you restrict the movement of the molecules inside. When you release pressure, those molecules move around quicker, at greater distances and speeds, resulting in a more flowy...I guess that's the world...yeah, more flowy gas.

Problems:

(WILL BE ADDED LATER)

Unit 3, Lessons 9 and 10

Lesson 9:

This lesson told us all about pressure, which can be defined simply as the force with which particles in a sample of gas hit the sides of their container. Pressure is related to temperature and volume through the use of three laws: Boyle's, Charles's, and Gay-Lussac's. There exists a thing called atmospheric pressure, or atm, which is pressure that constantly weighs on everything on a planet's surface. Earth's typical atm is around 14.7 and can increase/decrease when you're at sea level or on top of a mountain.

Problems:

(WILL BE ADDED LATER)

Lesson 10:

You can use Boyle's law to help calculate varying pressures when volume is constant. When volume doesn't change, it's greatly possible that a gas sample is in a rigid container, or one that doesn't change size/shape, like a graduated cylinder, a bowl, box, or a beaker. The following equation represents Boyle's law:

k = PxV

where k is your proportionality constant, or a value that stays the same in all calculations using Boyle's law. With this equation, you know that pressure and volume are indirectly proportional. When pressure increases, volume decreases, and vice versa.

Problems:

(WILL BE ADDED LATER)

Unit 3, Lesson 8

We've already discussed how molecules in samples of matter are in constant motion. However, some move slower than others, and particle speeds mean that we get these nifty things called phases. A phase is a physical change that matter goes though and can be solid -> liquid (melting), liquid -> solid (freezing), liquid -> gas (evaporation), or solid -> gas (sublimation.) Matter also has density. Depending on its phase, a sample can have a different density. For example, as I've already briefly touched on, ice is a phase of water and it is more dense than liquid water. Snow is less dense than water, even though it's frozen, because it has smaller pieces and you'd need more of it to equal the volume or density of  its solid/liquid counterparts.

Problems:

(WILL BE ADDED LATER)