regents chemistry

Regents ChemistryRegents Chemistry

11/05/2008Mrs. Nephew11/05/2008

Mrs. Nephew

Measuring HeatMeasuring Heat

The amount of heat given off or absorbed in a rxn can be calculated by:

q=mC∆Tq=heat (Joules)m=mass of the substanceC=specific heat capacity of substanceT=(Temp initial-Temp final)

The amount of heat given off or absorbed in a rxn can be calculated by:

q=mC∆Tq=heat (Joules)m=mass of the substanceC=specific heat capacity of substanceT=(Temp initial-Temp final)

Ex. How many joules are absorbed when 50 g of water are heated from 30.2C to

58.6C?

Ex. How many joules are absorbed when 50 g of water are heated from 30.2C to

58.6C?

Substitute the known values into the equation q=mC∆T .

Substitute the known values into the equation q=mC∆T .

Ex. How many joules are absorbed when 50 g of water are heated from 30.2C to

58.6C?

Ex. How many joules are absorbed when 50 g of water are heated from 30.2C to

58.6C?

Substitute the known values into the equation q=mC∆T .

Q=5936J=5.94 x 103J

Substitute the known values into the equation q=mC∆T .

Q=5936J=5.94 x 103J

CalorimeterCalorimeter

An insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process.

Remember in lab we used a “coffee cup calorimeter” earlier in the semester?

An insulated device used for measuring the amount of heat absorbed or released during a chemical or physical process.

Remember in lab we used a “coffee cup calorimeter” earlier in the semester?

In a calorimeter, the heat gained by the water is equal to the heat lost by the metal. That amount can be calculated using the calculation we just learned.

By measuring the temp increase of the water, the heat given off in a reaction can be calculated.

In a calorimeter, the heat gained by the water is equal to the heat lost by the metal. That amount can be calculated using the calculation we just learned.

By measuring the temp increase of the water, the heat given off in a reaction can be calculated.

ThermochemistryThermochemistry

The study of heat changes that accompany chemical reactions and phase changes.

The study of heat changes that accompany chemical reactions and phase changes.

We can’t determine the amount of heat required to melt or boil a substance. Temperature remains constant during a phase change, so there is no ∆T, so we can’t use our equation.

We can’t determine the amount of heat required to melt or boil a substance. Temperature remains constant during a phase change, so there is no ∆T, so we can’t use our equation.

Heat of FusionHeat of Fusion

The amount of heat needed to convert a unit of a substance from solid to liquid at its melting point.

Heat of fusion of water at 0C and 1 atm is 334 J/g.

No change in kinetic energy, no change in temperature.

The amount of heat needed to convert a unit of a substance from solid to liquid at its melting point.

Heat of fusion of water at 0C and 1 atm is 334 J/g.

No change in kinetic energy, no change in temperature.

MeltingMelting

Endothermic (requires heat).So freezing would be exothermic-

in freezing water releases 334J/g of heat and its potential energy decreases.

Endothermic (requires heat).So freezing would be exothermic-

in freezing water releases 334J/g of heat and its potential energy decreases.

Ex. How many joules are required to melt 255 g of

ice at 0C?

Ex. How many joules are required to melt 255 g of

ice at 0C?

Multiply the heat of fusion by the total mass of ice to determine the heat required.

Q= (255g)(334 J/g)=85,170 J =85.2 kJ

Multiply the heat of fusion by the total mass of ice to determine the heat required.

Q= (255g)(334 J/g)=85,170 J =85.2 kJ

Heat of VaporizationHeat of Vaporization

The amount of heat needed to convert a unit mass of a substance from its liquid phase to its vapor phases at constant temperature.

The amount of heat needed to convert a unit mass of a substance from its liquid phase to its vapor phases at constant temperature.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

As heat is added, the particles absorb sufficient energy to overcome the attractive forces holding them in the liquid phase.

The potential energy of the system increases and the temp remains constant.

Endothermic process.

As heat is added, the particles absorb sufficient energy to overcome the attractive forces holding them in the liquid phase.

The potential energy of the system increases and the temp remains constant.

Endothermic process.

Condensation is the reverse of boiling. It is an exothermic process.

Condensation is the reverse of boiling. It is an exothermic process.

Heat of vaporization of water at 0 C and 1 atm is 2260 J/g.

Heat of vaporization of water at 0 C and 1 atm is 2260 J/g.

How many joules of energy are required to vaporize 423 g of water at 100 C and 1 atm?

How many joules of energy are required to vaporize 423 g of water at 100 C and 1 atm?

Multiply the heat of vaporization by the total mass of water to determine the heat required.

Q=(423g)(2260J/g)=955,980 J=956J

Multiply the heat of vaporization by the total mass of water to determine the heat required.

Q=(423g)(2260J/g)=955,980 J=956J

Behavior of GasesBehavior of Gases

Kinetic molecular theoryA model or theory that is used to explain the behavior of gases.

It describes the relationships among pressure, volume, temperature, velocity, frequency, and force of collisions.

Kinetic molecular theoryA model or theory that is used to explain the behavior of gases.

It describes the relationships among pressure, volume, temperature, velocity, frequency, and force of collisions.

Kinetic TheoryKinetic Theory

Relates pressure and the number of collisions per unit time for a gas.

Relates pressure and the number of collisions per unit time for a gas.

Discovery LabDiscovery Lab

Balloon Experiment

Let’s demonstrate the relationship between temperature and volume of a gas in a closed system.

Balloon Experiment

Let’s demonstrate the relationship between temperature and volume of a gas in a closed system.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture. QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Let’s try a worksheet on calculating heat…

Let’s try a worksheet on calculating heat…

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.