Test #5
Avogardo's Hypothesis
- states that equal volumes of gasses at the same temperature and pressure contain an equal number of particles -whether the particles are large or small, large expanses of space exist between the individual particles of gas
Calorie
- the amount of energy (heat) required to raise the temperature of 1g of water 1*C - 1 calorie is 4.184 Joules
Rules for Solving Stoichiometry Problems
- write a balanced chemical equation - write down known amounts under each chemical - put a ? and unit by chemical question - perform stoichiometry calculation to determine amount
Mole-Interpretation
1 mole of ethanol reacts with 3 moles of oxygen to produce 2 moles of carbon dioxide and 3 moles of water
Molecular Interpretation
1 molecule of ethanol reacts with 3 molecules of oxygen to produce 2 molecules of carbon dioxide and 3 molecules of water
Change the molecular formula to an Empirical Formula: C6H12O6
CH2O
Percent Yield
The actual Amount of a given product as the percentage of the theoretical yield
What is Temperature
average kinetic energy of particles of a substance
Water Vapor Condenses on a cold pipe
exothermic
Your hand gets cold when you touch ice
exothermic
Pressure is produced by
gas molecules colliding with the walls of their container
Specific Heat Capacity
the energy required to change the temperature of 1 gram of a substance by 1 C degree
Morphine, derived from opium plants, has the potential for use and abuse. It's formula is C17H19NO3. What percent, by mass, is the carbon in this compound?
* look at notes
The composition of adipic acid is 49.3% C, 6.9% H, and 43.8% O (by mass). What is the empirical formula?
* look at notes
Using Mass Percent of an Element: For iron in iron(III) oxide, (Fe2O3)
* look at notes
if 6 moles of Fe are mixed with 5 moles of O2, which reactant is limiting
* look at notes
Pressure depends on...
- number of gas molecules - temperature of the gas volume the gas occupies
Energy required to change the temperature of a substance depends on
- the amount of the substance being heated (#of grams) - the temperature change (# of degrees) - the identity of the substance
Excess Reactant
- the excess reactant is the reactant the remains when the reaction stops - there is always left over excess reactant
Heats of Reaction
- the heat of reaction is the enthalpy change for chemical reactions exactly as it is written * heats of reaction are reported as △H * the physical state of the reactants and products must also be given * The standard conditions are that the reaction is carried out @ 101.3 kPa (1 atm) and 25 *C
Limiting Reactant
- the limiting reactant that limits the amount of product that can be made - the reaction stops when the limiting reactant is used up
Theoretical Yield
- the maximum amount of a given product that can be formed when the limiting reactant is completely consumed
Vapor Pressure
- the measure of the force exerted by a gas above a liquid - In a system at constant vapor pressure, dynamic equilibrium exists between the vapor and the liquid. The system is in equilibrium bc the rate of evaporation of the liquid equals the rate of condensation of vapor
THe Mole Volume Relationship
- the mole is a the center of your chemical calculations * to convery from one unit to another, you must use the mole as an intermediate step
Units of Pressure
- the simplest unit of pressure is the atmosphere (atm), the average pressure at sea level - a second unit of pressure, the millimeter of mercury originates from how pressure is measures with a barometer - average atmospheric pressure at sea level pushes a column of mercury to a height of 760 mm j
Volume of a Gas
- varies with a change in the temperature or a change in the pressure - the volume of a gas is usually measured at standard temperature and pressure
Boling Point
- when a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil * the temp at which the vapor pressure of the liquid is just equal to the external pressure on the liquid is boiling point (bp)
Atm - Torr
1 Atm = 760 Torr
Mass Calculations
1. balance the equation 2. convert the masses of the reactants or products to moles 3. use the balanced equations to se up the appropriate mole ratio(s) 4. use the mole ratio(s) to calculate the # of the moles of the desired reactants or products 5. convert from moles back to masses s
How to determine the Limiting Reactant of a Reaction
1. write and balance the chemical equation for the equation 2. concert known masses of reactants to moles (if applicable) 3. use the number of moles of reactants and the appropriate mole ratios determine which reactant is limiting
Evaporation in an Open Container
molecules that evaporate can escape from the container
System
part of the universe on which we wish to focus attention
Measure of pressure
measure = force/ area
To calculate the energy required for a reaction or process: Heat Energy Required: q=s x m x △T
q- energy(heat) required (Joules, J) s- Specific heat capacity (J/C) m- mass (g) △t- change in temperature (C) where △t = (T1-T2)
When adding the same amount of energy to two similar mass samples, the substance with the larger specific heat will have a _________ temp. change
smaller
Actual Yield
the amount of product that actually for when the reaction is carried out the laboratory
Normal Boiling Point
because a liquid can have various boiling points depending on pressure, normal boiling point is defined as the boiling point of a liquid at a pressure of 1 atm
The ice gets warmer when you touch it
endothermic
Law of Conservation of Energy
energy can be converted from 1 form to another but can be neither created nor destroyed * the total energy content of the universe is constant
Why does 1 mole of any gas occupy the same volume (22.4 L) at standard temperature and pressure
gas molecules do vary in size, just like molecules of solids and liquids, but the particles in a gas are always so far apart that the change in volume of the molecules doesn't change the volume the gas occupied at STP
Surroundings
includes everything else in the universe - energy gained by the surroundings must be equal to the energy lost by the system
Vaporization
the conversion of a liquid to a gas or vapor - when such a conversion occurs at the surface of a liquid that is not boiling the process is known as evaporation
Mole-Ratio
the mole ratio allows us to convert from moles to one substance in a balanced equation to moles of a second substance in the equation
Evaporation in a Closed Container
the molecules can not escape. they collect as vapor above the liquid and some molecules will condense back to liquid
Molar Volume of Gas
the quantity of 22.4 L is called the molar volume of gas
Common energy Units for Heat
Calorie and Joule
Increase In Pressure is due too
- more frequent collisions - higher energy collisions
Water Boils on a kettle being heated on a stove
Endothermic
A gaseous compound containing carbon and hydrogen was analyzed and found to consist of 83.65% carbon by mass. Determine the empirical formula of the compound.
* look at notes
Calculate the amount in kJ required to decompose 2.24 mol NaHCO3 (s): 2NaHO3 (s) + 85kJ = Na2Co3(s) + H2O (L) CO2 (g)
* look at notes
Calculate the number of moles of NI3 that can be made from 5.50 mole N2 in the reaction
* look at notes
Example with STP conversion
* look at notes
How many g of chromium (III) oxide can be produced from 15 g of solid chromium an excess oxygen fas
* look at notes
How many g of tin (II) Flourise can be made from 55 g of Hydrogen Flouride if there is plenty of tin available to react
* look at notes
If 10 moles of H2 are reacted with 6 moles of O2 and the reaction goes to completion which reactant is limiting
* look at notes
If 50g of Silicon dioxide is heated with an excess carbon, 27.9 g of Silicon Carbide (sic) is produced
* look at notes
If 80 g of I2O5 reacts with 28 g of Co2 what is the LR?
* look at notes
Mass percent of an element
* look at notes
Empirical Formula
- E.F - represents the smallest ratio of atoms present in a compound (simplest whole number ratio)
Molecular Formula
- M.F - gives the total number of atoms of each element present in one molecule of a compound * the "true" formula * Molecular Formula = (Empirical Formula)n where n is the integer
Information Given by Chemical Equations
- a balanced chemical equation gives realtive numbers (or moles) of reactants and product molecules that participate in a chemical reaction
Energy
- ability to do work or product heat - heat involves a transfer of energy between two objects due to temperature difference
Percent Yield
- an important indicator of the efficiency of a particular laboratory or industrial reaction - a batting average is a percent yield
Vapor Pressure and Temperature Change
- an increase in the temperature of a contained liquid increases the vapor pressure - the particles in the warmed liquid have increased Kinetic energy as a result, more of the particles will have the minimum kinetic energy necessary to escape the surface of the liquid
Kinetic Molecular Theory
- assumptions * gases consist of tiny particles (insignificant volumes) * The distance between particles is large compared with the size of the particles * Gas particles have no attraction for each other * Gas particles move in straight lines in all directions colliding frequently with each other and with the walls of their container * Collisions are perfectly elastic (no energy lost in collision) * the average kinetic energy for particles is the same for all gases at the same temperature * the average kinetic energy is direcly porportional to the kelvin temperature
Boiling Point and Pressure
- bc a liquid boils when its vapor pressure is equal to the external pressure, liquids don't always boil at the same temperature * a lower external pressure the boiling point decreases * a higher external pressure the boiling point increases
Enthalpy Change
- depends on whether the reaction is exothermic or endothermic - in an exothermic reaction, the enthalpy chance can be considered a product and negative
Exothermic Process
- energy flows out of a system - liquid to a solid - gas to liquid
Endothermic Process
- heat flow is into a system - system absorbs energy from surroundings - solid to liquid - liquid to gas
Thermochemical Equations
- in a chemical equation, the enthalpy change for the reaction can be written as either a reactant or a product
Standard Temperature and Pressure (STP)
- means a temperature of 0*C and a pressure of 1 atmosphere (atm) - at 1 STP, 1 mole representative particle of any gas occupied a volume of 22.4 L
How can a puddle of water evaporate at room temperature
-some fast moving particles leave the liquid phase to gas - once these fast particles leave, the rest of the liquid will loose volume causing the temperature of the water to increase - because of the added heat new water molecules will begin to evaporate starting the cycle over again
Change the molecular formula to an Empirical Formula: CH2O
E.F - C2HO
Stoichiometry
deals with the quantitative relationship between the reactants and products in a balanced equation
If you change the temperature of a sample of gas from 50C to 25C at a constant volume the pressure of the gas will...
decrease