Chemistry Test 5-1-2015 – Flashcards
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Energy is equal too....
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Enthalpy and Heat
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Thermochemistry
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The study of changes im heat in chemical reactions
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Temperature
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Average motion of molecules
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Heat
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Transfer of energy
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Heat always travels from...
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High to low concentration
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Exothermic reactions
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Produce heat,will be in product. Heat,like energy, is measured in joules
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Endothermic reactions
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Consume heat in order for the reaction to go forward
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Enthalpy
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Is the sum of potential(stored) and kinetic(used) energy of a system
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Delta H
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A change in enthalpy signals a change in energy for the system (energy has been absorbed or released)
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If Delta H is positive then the reaction is...
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Absorbed(Endothermic)
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If Delta H is negative then heat is...
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Let go(Exothermic)
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Hess's Law
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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
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Calorimetry
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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*
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Heat capacity
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Amount of heat needed to raise the temperature of an object by 1 degree Celsius
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Specific heat
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Heat capacity of 1 gram of a substance
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General equation for finding heat?
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Mass * delta tempuratue* specific heat
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Specific heat of water?
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4.184 joules/grams * Celsius
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Finding Delta H for a reaction?
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Qrxn= -qsur Or Qsur=-qrxnThe heat transfered in a reaction, qrxn, is equal in magnitude but opposite in sign to the heat absorbed by the surrounding
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Good conductors have..
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Lower heat capacity The ability to transfer energy quickly Allows them to transer(or gain) heat easily
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Insulators
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Take large amounts of energy to heat or cool (Water,antifreeze)
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1 calorie equals how many joules?
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4.184 joules
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1 Cal equals how many calories?
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1 Cal= 1000 calories
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How many joules in 1 Cal?
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1 Cal= 4184 joules
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Food labels are measured in..
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The amount of energy to consume this amount of food
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If the total number of calories is not "burned" then...
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They are stored by the body
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Different types of food contain...
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Different amounts of energy(Different types of bonds)
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Carbohydrates/Proteins are how many kJ's and how many Cal's?
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17 kJ/g and 4 Cal/g
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Fats are how many kJ's and how many Cal's?
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38 kJ/g and 9 Cal/g
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Why does your body store unused proteins(cabrs) as fats?
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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
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Which has more energy: a pound of fat or a pound of carbs(Proteins)?
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A pound of fat
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How many calories are in 1 pound (454 grams) of fat?
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4086 calories
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How many calories are in 1 pound(454 grams) of proteins/Carbohydrates?
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1816 calories
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The prefix exo- in the word exothermic means?
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Outside
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Combustion reactions (burning hydrocarbons) would be classified as
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Exothermic
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The study of heat flow and heat measurement is called
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Calorimetry
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______ law describes how to find the net enthalpy changes for a series of reactions
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Hess's law
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The amount of heat needed to raise the temp. Of a container of water (of any size) from 14 degrees to 15 degrees is
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Heat capacity
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A reaction that has a positive enthalpy can be described as...
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Endothermic
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If the coeficcients of a balanced equation are doubled, the enthalpy change for the reaction is
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Doubled
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Heat
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The energy that is transferred from one object to another
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Joule
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The SI unit for energy
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Combustion
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Example of an exothermic reaction
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T or F It is "energy" that maintains your body temperature close to 37 degrees
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True
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T or F "Bond breaking" in a chemical reaction releases energy
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False Bond forming
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T or F Heat is transferred between two objects that are "the same temperature"
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False Different
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T or F An "exothermic" reaction absorbs heat from the environment
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False Endothermic
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T or F All combustion reations are "exothermic"
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True
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T or F If a reaction is endothermic, the amount if heat appears on the "right" side of the arrow in the balanced equation
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False Left
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T or F Energy can be stored in the "chemical bonds" of a substance
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True
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Provide two examples from daily life that demonstrates how heat us transferred from one object to another
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Holding hands Camp fires Cooking food Opening a refrigerator Straightening hair
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Why is the joule the SI unit for energy and heat?
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Because heat is the flow of energy
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Provide an analogy that explains why bond breaking requires energy
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Force's of energy are required to break things (Ex. Putting hands together/pulling them apart)
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When ammonium chloride dissolves in a beaker of water, the beaker becomes cold to touch. Why?
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All of the heat energy was absorbed and used up in the reaction (endothermic)
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What does Hess's law say about the enthalpy changes for a net reaction?
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Enthalpy for a net reaction can be determined by summing up all of the enthalpys for the individual steps
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Explain why Hess's law is useful in the chemistry lab
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It allows for enthalpy to be calculated for reactions that can not be performed directly
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How can enthalpy be calculated for an equation where the coefficients have be doubled?
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Double the enthalpy as well
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What happens to enthalpy if a reaction is reversed?
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Signs are changed Ex: positive to negative Or Negative to positive
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Can a reaction proceed in more then one direction?
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Yes because energy can go in reverse
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Heat of Fusion
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The amount of heat required to move from solid to liquid states
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Heat of vaporization
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The amount of heat required to move from liquid to gas states
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The heat absorbed or released in a reaction depends on a quantity called...
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Energy
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The enthalpy of a substance is similar too, but not exactly the same as, the....
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Energy
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The symbol Delta H litterally means a " " in enthalpy
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Change
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The delta H for an " " reaction will always be a positive sign
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Endothermic
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In an exothermic reactions, products will always be " " than reactants.
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Less
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Conditions such as temperature, " ", and the physical states of the substances in a reaction can affect delta H
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Pressure
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The enthalpy change measured at 1 atm and 25 degrees Celsius,when the reactants and products are in their standard states, is called a " "
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Standard enthalpy change
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You must know the number of " " of reactants involved in a reaction to calculate delta H
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Moles
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How is enthalpy of a substance related to the energy of a substance?
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The enthalpy os a substance is simillar but not exactly the same as the energy of a substance
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If you were given delta H of a reaction could you determine wheter the reaction was exothermic or endothermic?
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Yes, if delta H is positive then the reaction is endothermic. If delta H is negative them the reaction is exothermic
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Compare the enthalpy of the reactants and the products in both exothermic and endothermic reactions.
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Products are lower than that of reactants for exothermic reactions
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What is meant by the standard state of an element?
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Most stable form of an element under standard conditions (1 atm and 25 degrees celsius)
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The study of heat flow and heat measurement is called....
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Calorimetry
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The words calorimeter ,calorimetry, and calorie are all derived from the Latin word calor, which means....
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Heat
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The amount of heat needed to raise an objects temperature depends on its ....
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Heat capacity
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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....
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Specific heat
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" " has one of the highest specific heats of any common substance
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Water
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A transfer of heat is detected by measuring a " " change
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Tempuratue
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A " " is a well insulated container used to measure temperature changes
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Calorimeter
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On the average, " " suppy 17j/g*c (4 Cal/g) of energy
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Carbohydrates
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Foods are reacted with " " in a labratory calorimeter to determine there energy values
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Oxygen
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Ti means
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Initial temperature
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Tf means
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Final temperature
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Qrxn means
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Q reaction
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Qsur means
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Q of surrounding
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m means
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Mass
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C means
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Cal
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Explain how a calorimeter is used to determine the quantity of heat transferred in a chemical reaction.
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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
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BONUS Who's the coolest person you know?
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Johniah :3
