Gen Chem Exam 3 Flashcards
What undergoes combustion during the welding of metals?
A mixture of acetylene and oxygen
What is more practical and convenient to measure compared to moles?
Mass
Limiting Reactant
- The substance that is used up first
- The substance that limits the amount of product that can form.
Excess Reactant
The reactants that do not completely react and are left over at the end of the reaction.
What reactant yields the smallest amount of product?
Limiting reactant
Theoretical Yield
The maximum amount of product, which is calculated using the balanced equation and the limiting reactant.
Actual Yield
The amount of product experimentally obtained or collected during the experiment.
Percent Yield
The ratio of actual yield to theoretical yield.
Percent Yield Formula
Actual Yield/Theoretical Yield x 100%
During what 3 scenarios does energy change occur?
- When reactants interact
- When bonds break apart
- When products form
Heat of Reaction / Enthalpy Change
The difference between the enthalpy of the products and enthalpy of the reactants
Exothermic Reaction
- Heat is released
- The energy of the products is less than the energy of the reactants
- Heat is a product
Endothermic Reactions
- Heat is absorbed
- The energy of the products is greater than the energy of the reactants
- Heat is a reactant
Cold packs being activated are an example of a ___ reaction.
endothermic
How many elements in the periodic table exist as gases at room temperature conditions?
Only a few
What elements are considered gases at room temperature conditions?
- All noble gases
- Some diatomic molecules (H2, N2, O2, F2, and Cl2)
- Oxides of the nonmetals
(CO, CO2, NO, NO2, SO2, and SO3)
What are the 7 properties of gases?
- Indefinite shape and volume
- Takes the same shape and volume as its container
- Particles are far apart
- Particles are moving quickly in random directions
- Low densities
- Compressible
- Form homogenous mixtures
Kinetic Molecular Theory of Gases
- Gases consist of tiny particles moving randomly at high velocities
- Most of the volume of a gas is empty space.
- There are no attractive or repulsive forces between gas particles
- Gas particles are constantly moving in straight paths.
- The average kinetic energy of the gas particles is proportional to the kelvin temperature of the sample.
What causes gas pressure to arise?
Collisions exerted by gas particles against the container walls.
What four units are used to measure pressure?
- Pascal (Pa)
- mmHg
- Torr
- Atmosphere (atm)
Atmosphere
A mixture of gases that cover the earth
Atmospheric Pressure
The pressure exerted by a column of this air mixture towards the surface of the Earth.
When is atmospheric pressure (atm) at 1?
Sea level
How many mmHg and Torr are in 1 atm?
760
Barometer
Measures the pressure exerted by the gases in the atmosphere.
What causes atmospheric pressure to change?
- Weather
- Altitude
What weather causes the atmospheric pressure to increase?
Hot and sunny
What weather causes the atmospheric pressure to decrease?
Rainy
Atmospheric pressure decreases as ___ increases.
Altitude
What are the 4 variables that define the physical properties of a gas?
- Pressure (P)
- Temperature (T)
- Volume (V)
- Amount of gas moles (n)
What are the 4 gas laws?
- Boyle’s Law
- Charles’s Law
- Gay-Lussac’s Law
- Avogadro’s Law
Ideal Gas Law Definition
A gas whose behavior follows the 4 gas laws.
Ideal Gas Law Formula
PV = nRT
What does the variable R represent in the ideal gas law formula?
The gas constant (value is given on sheet)
What type of volumes do cylinders have?
A fixed volume (can’t be greater than 1 atm)
What happens to the volume when you blow up a balloon?
The volume will expand until the pressure equalizes with the atmospheric pressure.
Combined Gas Law Definition
When more than two properties of gas change at once, two laws can be combined to explain its behavior.
Combined Gas Law Equation
(P1 x V1)/T1 x (P2 x V2)/T2
Boyle’s Law
V decreases as P increases
- n and T are constant
Charles’s Law
V changes the same to T
- n and P are constant
Gay- Lussac’s Law
P changes the same to T
- n and V are constant
What causes vapor to form?
When liquid molecules with enough kinetic energy break away from the surface of a liquid.
What happens when liquid is left in an open container?
It will eventually evaporate
What happens when vapor is left in a closed container?
The vapor accumulates and creates pressure called vapor pressure.
What is vapor pressure of a liquid dependent on?
Temperature
Boiling Point
The temperature at which the vapor pressure (inside container) becomes equal to the external pressure.
Water boils at ___ temperatures in the mountains.
lower
Avogadro’s Law
V changes the same to n
- P and T are constant
What are the standard conditions for the gas formulas?
T = Kelvin
V = L
n = Moles
P = atm
Why do the gas formulas need to be converted with the same units?
So comparisons can be made among different experiments.
What is the standard volume at 1 mole of gas?
22.4 L (molar volume)
What does the molar volume mean?
No matter the identity of the gas, the volume is ALWAYS 22.4 L at 1 mole.
Dalton’s Law of Partial Pressures
The total pressure exerted by a mixture of gases in a container at constant V and T
The sum of the pressures of each individual gas in the container
Partial Pressure
A gases own pressure in comparison to the total pressure of the gas.
Partial Pressure Formula
P total = P1 + P2 + P3 + Pn…
What are the different elements within the air we breath?
- N2 (78%)
- O2 (21%)
- other gases (1%)
What is the partial pressure exerted by a given gas proportional to?
The mole percentage of that gas in the mixture.
What are the 4 IMFs?
- Ion Dipole
- Hydrogen Bonding
- Dipole-Dipole
- Dispersion
Aqueous Solution (aq)
Dissolved in water
Solutions
Homogenous (completely mixed) mixtures of 2+ substances
What are the two components of solutions?
- Solvents
- Solutes
Solvent
Present in a larger amount
- major component of the slution
Solute
Present in a smaller amount
- spread evenly throughout the solution
___ dissolves into ___ to form a solution.
Solute, solvent
What physical states can a solute have?
Liquid, gas or solid
How can solutes be seperated?
Evaporation
- not by filtration
Are solutes visible?
No but they can add a color to the solution
What causes the solute to dissolve into the solvent?
Molecules within the solvent are capable of forming sufficient attractions with the solute particles to make them dissolve
Water (H2O)
- A polar molecule due to O-H bonds
What is one of the most common solvents in nature?
Water
What do solute molecules form with water?
Intermolecular forces
What takes place in water media?
The vast majority of chemical reactions (biological reactions)
Aqueous Reactions
Reactions that take place in water media
What combinations causes solutions to form?
Polar - Polar
Nonpolar - Nonpolar
What are the 3 common nonpolar solvents?
- Hexane (C6H12)
- Toluene (C7H8)
- Carbon Tetrachloride (CCL4)
Do nonpolar solutes dissolve in polar solvents?
NO
- Nonpolar outweighs the polar
What are the 2 examples of nonpolar solutes?
- Hydrocarbons, oils, and fats
- Compounds that can only form dispersion forces (cancel out)
Hydrocarbons
Compounds with only hydrogen and carbon
What happens when there is an absence of attractions?
A solution cannot form due to insufficient energy levels.
Nonpolar molecular compounds do not dissolve in….
Water
What are the 3 most common polar solvents?
- Water (H2O)
- Acetone ((CH3)2C=O)
- Ethanol (CH3CH2OH)
What are examples of polar solutes?
- Ionic compounds or salts
- Compounds that can form dipole-dipole interactions and/or Hydrogen Bonding
Within a lewis structure, hydrogen bonds are shown as…
dashed lines
Are polar molecular compounds, such as menthol, soluble in water?
Yes
- There is a polar OH- group present to form H bonds in water
What are 2 examples of polar molecular compounds?
- Small polar molecules
- Water soluble vitamins
Ionic Solutes
Form ion dipole interactions with water molecules.
What is an example of an ionic solute?
NaCl crystals
What happens during the ionic solute of NaCl crystals?
- Na+ and Cl- ions are pulled out into the solution and get dissolved