Chemistry Chapter 11 Thermochemistry

Front 1

melting ice and boiling water _______ water

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absorb

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thermochemistry

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concerned with the heat changes that occur during chemical reactions

Front 3

energy

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the capacity for doing wrk or supplying heat

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unlike matter, energy is

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weightless, odorless, and tasteless

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energy stored within the structural units of chemical substances

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chemical potential energy

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what contains a significant amount of chemical potential energy

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gasoline

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dfference substances store

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diferent amounts of energy

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what determines the amount of energy stored in the substance

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the amount of energy and their arrangement in the substance

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what is represented by q

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heat

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what is the energy that transfers from one object to another because of a temperature difference between them

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heat

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heat cannot be detected by

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the senses or by instruments

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only ______ caused by heat can be detected

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changes

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one of the effects of adding heat is

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a rise in the temperature of objects

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heat always flows from a

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warmer objecct to a cooler object

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what happens if two objects remain in contact

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heat will flow from the warmer object to the cooler object until the temperature of both objects is the same

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all chemical reactions and changes in physical state involve

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either the release or the absorption of heat

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in studying heat changes, it is useful to define a _______ as the part of the universe on which you focus your attention

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system

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includes everything else in the universe

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the surroundings

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what is a good approximation to consider in thermochemical experiments

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the region in the immediate vicinity of the system as the surroundings

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together, the system and its surroundings constitute the

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universe

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what is a major goal of studying thermochemistry

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to examine the flow of heat from the system to its surroundings, or the flow o heat from the surroundings to the system

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states that in any chemical or physical process, energy is neither created nor destroyed

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law of conservation of energy

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all of the energy involved in a process can be accounted for as

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work, stored energy, or heat

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in thermochemical calculations the direction of the heat flow is given from

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the point of view of the system

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heat flowing into a system from its surroundings is defined as

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positive

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a process that absorbs heat from the surroundings is called an

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endothermic process

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what happens in an endothermic process

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the system gains heat as the surroundings cool down

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heat flowing out of te system into its surroundings is

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negative

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a process that releases heat to its surroundings is called an

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exothermic process

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what occurs in an exothermic process

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the system loses heat as the surroundings heat up

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exothermic (chart)

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heat flows out of the system

heat change < 0 (negative)

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endothermic

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heat flows into the system

heat change > 0 (positive)

Front 33

what does it mean to "burn calories"

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during exercise, your body generates heat, and this heat is measured in units called calories

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how is the heat generated in your body

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as your body breaks down sugars and fats into carbon dioxide and water

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what accomplishes the same result as if there were an actual fire burning the sugars and fats within your body

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chemical reactions

Front 36

In breaking down 10 grams of sugar, your body generates a certain amount of heat.

When would the same amount of heat be produced?

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if 10 grams of sugar were completely burned in a fire, producing carbon dioxide and water.

Front 37

what is defined as the quantity of heat needed to raise the temperature of 1 gram of pure water 1 *C

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a calorie

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what refers to the energy in food

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dietary Calorie

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when are calories not used

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when referring to energy contained in food

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1 dietary Calorie =

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1 kilocalorie

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1 kilocalorie =

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1000 calories

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what does the statement "10 grams of sugar has 41 Calories" mean

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that 10 grams of sugar releases 41 kilocalories of heat when completely burned to produce carbon dioxide and water

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what is a calorie related to

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a joule

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what is the SI unit of heat and energy

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joule

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who is the joule named after

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English physicist James Prescott Joule

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a joule is slightly less than _____ of a calorie

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1/4

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1 joule of heat raises the temperature of 1 gram of pure water

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0.2390 *C

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1 J =

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0.2390 cal

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4.184 J =

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1 cal

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the amount of heat needed to increase the temperature of an object exactly 1 *C is the ___________ of that object

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heat capacity

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what does the heat capacity of an object depend on

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its mass as well as its chemical composition

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the greater the mass of an object

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the greater its heat capacity

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different substances with the same mass may have

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different heat capacities

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_________________ or _________ of a substance is the amount of heat it takes to raise the temperature of 1 g of the substance 1 *C

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specific heat capacity
specific heat

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what has a very high specific heat compared to other substances in the table

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water

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what has low specific heats

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metals

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Heat affects the temperature of objects with a high specific heat much less than

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the temperature of those with a low specific heat

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just as it takes a lot of heat to raise the temperature of water,

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water also releases a lot of heat as it cools

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how do you calculate the specific heat of a substance

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you divide the heat input by the temperature change times the mass of the substance

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q

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heat

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m

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mass

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C

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specific heat

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delta T

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change in temperature

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how is delta T calculated

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delta T = Tf - Ti

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Tf

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final temperature

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Ti

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initial temperature

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C =

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q / m x delta T

heat(joules or calories) / mass(g) x change in temp (*C)

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specific heat may be expressed in terms of

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joules or calories

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units of specific heat

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J/(g x *C)

cal/(g x *C)

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most physical and chemical changes you will encounter occur at

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constant pressure

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a variable that takes constant pressure into account

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enthalpy

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how can you measure the energy changes that accompany chemical and physical processes?

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by defining a thermodynamic variable

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heat that is released or absorbed during many chemical reactions can be measured by

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calorimetry

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the accurate and precise measurement of heat change for chemical and physical processes

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calorimetry

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in calorimetry, the heat released by the system is equal to

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the heat absorbed by its surroundings

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to measure heat changes accurately and precisely, the processes must be carred out in an

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insulated container

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the insulated device used to measure the absorption or release of heat in chemical and physical processes is called a

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calorimeter

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what is an example of an excellent heat insulator and why

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foam cups because they do not let much heat in or out

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for systems at constant pressure, the heat conents is the same as a property called _____ of the system

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enthalpy (H)

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heat changes for reactions carried out at constant pressure are the same as

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changes in enthalpy, symbolized as delta H

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q =

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delta H

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delta H =

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m x C x delta T

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q = delta H = m x C x delta T

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equation for the heat change in a chemical reaction carried out in aqueous solution

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delta H

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heat change

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the sign of delta H is negative for

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exothermic reaction

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the sign delta H is positive for

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endothermic reaction

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How do you measure the heat change for a reaction in aqueous solution in a foam cup calorimeter

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dissolve the reacting chemicals (the system) in known volumes of water (the surroundings)

then measure the initial temperature of each solution and mix the solutions in the foam cup

after the reaction is complete, measure the final temperature of the mixed solutions

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because you know the inital and final temperatures of water, you can calculate the

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heat released or absorbed in the reaction using the equation for specific heat

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calorimetry experiments can also be performed at constant pressure using a device called a

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bomb calorimeter

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measures the heat released from burning a compound

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bomb calorimeter

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the calorimeter is a ____ system

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closed

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what does "the calorimeter is a closed system" mean

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the mass of the system is constant

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you can treat heat change in a chemical reaction like any other

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reactant or product in a chemical equation

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an equation that includes the heat change is called a

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thermochemical equation

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the heat change for the equation exactly as its written

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heat of reaction

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you will usually see heats of reaction reported as

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delta H

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the standard conditions are that the reaction is carried out at

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101.3 kPa (1 atmosphere)

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if the reaction is endothermic, where does the heat change go in the equation

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left side

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if the reaction is exothermic, where does the heat change go in the equation

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right side

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the amount of heat released or absorbed during a reaction depends on

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the number of moles of the reactants involved

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the heat reaction for the complete burning of one mole of a substance

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heat of combustion

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in endothermic processes, the potential energy of the product is

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higher than the potential energy of the reactants