# Chemistry Test 5-1-2015

Energy is equal too….
Enthalpy and Heat
Thermochemistry
The study of changes im heat in chemical reactions
Temperature
Average motion of molecules
Heat
Transfer of energy
Heat always travels from…
High to low concentration
Exothermic reactions
Produce heat,will be in product. Heat,like energy, is measured in joules
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Endothermic reactions
Consume heat in order for the reaction to go forward
Enthalpy
Is the sum of potential(stored) and kinetic(used) energy of a system
Delta H
A change in enthalpy signals a change in energy for the system (energy has been absorbed or released)
If Delta H is positive then the reaction is…
Absorbed(Endothermic)
If Delta H is negative then heat is…
Let go(Exothermic)
Hess’s Law
If series of reactions are added together, the enthalpy change for the net equation will be the sum of the enthalpy changes for the individual steps
Calorimetry
The study of heat flow and heat measurement
*Calorimetry experiments can determine heat of reactions, or enthalpy changes, by making accurate measurements of temperature changes in a calorimeter*
Heat capacity
Amount of heat needed to raise the temperature of an object by 1 degree Celsius
Specific heat
Heat capacity of 1 gram of a substance
General equation for finding heat?
Mass * delta tempuratue* specific heat
Specific heat of water?
4.184 joules/grams * Celsius
Finding Delta H for a reaction?
Qrxn= -qsur
Or
Qsur=-qrxn

The heat transfered in a reaction, qrxn, is equal in magnitude but opposite in sign to the heat absorbed by the surrounding

Good conductors have..
Lower heat capacity
The ability to transfer energy quickly
Allows them to transer(or gain) heat easily
Insulators
Take large amounts of energy to heat or cool
(Water,antifreeze)
1 calorie equals how many joules?
4.184 joules
1 Cal equals how many calories?
1 Cal= 1000 calories
How many joules in 1 Cal?
1 Cal= 4184 joules
Food labels are measured in..
The amount of energy to consume this amount of food
If the total number of calories is not “burned” then…
They are stored by the body
Different types of food contain…
Different amounts of energy(Different types of bonds)
Carbohydrates/Proteins are how many kJ’s and how many Cal’s?
17 kJ/g and 4 Cal/g
Fats are how many kJ’s and how many Cal’s?
38 kJ/g and 9 Cal/g
Why does your body store unused proteins(cabrs) as fats?
Since proteins(carbs) has 4 Cal per gram and fat has more (9 Cal per gram) the unused proteins are more efficiently stored as fat
Which has more energy: a pound of fat or a pound of carbs(Proteins)?
A pound of fat
How many calories are in 1 pound (454 grams) of fat?
4086 calories
How many calories are in 1 pound(454 grams) of proteins/Carbohydrates?
1816 calories
The prefix exo- in the word exothermic means?
Outside
Combustion reactions (burning hydrocarbons) would be classified as
Exothermic
The study of heat flow and heat measurement is called
Calorimetry
______ law describes how to find the net enthalpy changes for a series of reactions
Hess’s law
The amount of heat needed to raise the temp. Of a container of water (of any size) from 14 degrees to 15 degrees is
Heat capacity
A reaction that has a positive enthalpy can be described as…
Endothermic
If the coeficcients of a balanced equation are doubled, the enthalpy change for the reaction is
Doubled
Heat
The energy that is transferred from one object to another
Joule
The SI unit for energy
Combustion
Example of an exothermic reaction
T or F
It is “energy” that maintains your body temperature close to 37 degrees
True
T or F
“Bond breaking” in a chemical reaction releases energy
False
Bond forming
T or F
Heat is transferred between two objects that are “the same temperature”
False
Different
T or F
An “exothermic” reaction absorbs heat from the environment
False
Endothermic
T or F
All combustion reations are “exothermic”
True
T or F
If a reaction is endothermic, the amount if heat appears on the “right” side of the arrow in the balanced equation
False
Left
T or F
Energy can be stored in the “chemical bonds” of a substance
True
Provide two examples from daily life that demonstrates how heat us transferred from one object to another
Holding hands
Camp fires
Cooking food
Opening a refrigerator
Straightening hair
Why is the joule the SI unit for energy and heat?
Because heat is the flow of energy
Provide an analogy that explains why bond breaking requires energy
Force’s of energy are required to break things
(Ex. Putting hands together/pulling them apart)
When ammonium chloride dissolves in a beaker of water, the beaker becomes cold to touch. Why?
All of the heat energy was absorbed and used up in the reaction (endothermic)
What does Hess’s law say about the enthalpy changes for a net reaction?
Enthalpy for a net reaction can be determined by summing up all of the enthalpys for the individual steps
Explain why Hess’s law is useful in the chemistry lab
It allows for enthalpy to be calculated for reactions that can not be performed directly
How can enthalpy be calculated for an equation where the coefficients have be doubled?
Double the enthalpy as well
What happens to enthalpy if a reaction is reversed?
Signs are changed
Ex: positive to negative
Or
Negative to positive
Can a reaction proceed in more then one direction?
Yes because energy can go in reverse
Heat of Fusion
The amount of heat required to move from solid to liquid states
Heat of vaporization
The amount of heat required to move from liquid to gas states
The heat absorbed or released in a reaction depends on a quantity called…
Energy
The enthalpy of a substance is similar too, but not exactly the same as, the….
Energy
The symbol Delta H litterally means a ” ” in enthalpy
Change
The delta H for an ” ” reaction will always be a positive sign
Endothermic
In an exothermic reactions, products will always be ” ” than reactants.
Less
Conditions such as temperature, ” “, and the physical states of the substances in a reaction can affect delta H
Pressure
The enthalpy change measured at 1 atm and 25 degrees Celsius,when the reactants and products are in their standard states, is called a ” “
Standard enthalpy change
You must know the number of ” ” of reactants involved in a reaction to calculate delta H
Moles
How is enthalpy of a substance related to the energy of a substance?
The enthalpy os a substance is simillar but not exactly the same as the energy of a substance
If you were given delta H of a reaction could you determine wheter the reaction was exothermic or endothermic?
Yes, if delta H is positive then the reaction is endothermic. If delta H is negative them the reaction is exothermic
Compare the enthalpy of the reactants and the products in both exothermic and endothermic reactions.
Products are lower than that of reactants for exothermic reactions
What is meant by the standard state of an element?
Most stable form of an element under standard conditions
(1 atm and 25 degrees celsius)
The study of heat flow and heat measurement is called….
Calorimetry
The words calorimeter ,calorimetry, and calorie are all derived from the Latin word calor, which means….
Heat
The amount of heat needed to raise an objects temperature depends on its ….
Heat capacity
Every substance has a ” ” which tells you how much heat is necessary to raise the temperature of 1 gram of the substance by 1 Celsius degree….
Specific heat
” ” has one of the highest specific heats of any common substance
Water
A transfer of heat is detected by measuring a ” ” change
Tempuratue
A ” ” is a well insulated container used to measure temperature changes
Calorimeter
On the average, ” ” suppy 17j/g*c (4 Cal/g) of energy
Carbohydrates
Foods are reacted with ” ” in a labratory calorimeter to determine there energy values
Oxygen
Ti means
Initial temperature
Tf means
Final temperature
Qrxn means
Q reaction
Qsur means
Q of surrounding
m means
Mass
C means
Cal
Explain how a calorimeter is used to determine the quantity of heat transferred in a chemical reaction.
First, a Calorimeter takes the heat of water that is in it. After placing a metal in the water, the Calorimeter takes the difference between the last and first temperatures
(Tf-Ti) to find the amount of heat transferred
BONUS
Who’s the coolest person you know?
Johniah :3