Chapter 16

Chemistry

Energy is the ability to do work or produce heat

Energy stored in a substance because of its

composition

Calorie – amount of heat needed to raise the

temperature of 1g of water 1oC

Calorie = 1000 calories

Joule = SI unit of energy (4.18 J = 1 calorie)

The breakfast shown in the photograph contains 230

Calories. How much energy in joules will this

healthy breakfast supply?

230 Calories x 1000 = 230,000 calories

230,000 calories x 4.18 Joules = 9.6 x 105 Joules

464 KJ per

serving

Amount of heat required to raise the

temperature of 1g of any substance 1oC

The specific heat of water is 4.184J/g.oC

In the construction of bridges and skyscrapers, gaps must be left between adjoining steel beams to allow for the expansion and contraction of the metal due to heating and cooling. The temperature of a sample of iron with a mass of 10.0g changed from 50.4oC to 25oC with the release of 114J heat. What is the specific heat of iron?

Formula: Q = mcDTm = mass

c = specific heat

Dt = change in temperature

Q = Heat (energy)

Insulated device used to determine heat changes

A piece of metal with a mass of 4.68g

absorbs 256J of heat when its temperature

increases by 141oC. What is the specific heat

of the metal?

Can you identify the metal? Where do you

think you might find this kind of information?

Calculate the Difference!

What is the formula?

Find specific heat if a 8.5g object releases

113 J of heat energy with a temperature

change of 24 degrees Celsius.

Find how much heat is released if a 12g

object with a specific heat of .31 changes

from 55oC to 25oC.

System = specific part of universe that contains

the reaction

Surroundings = everything else in the

universe – the reaction

Universe is the sum of the system and its

surroundings

(H) is the heat content of a system at

constant pressure

It is the heat absorbed or released during a

chemical reaction

If a reaction releases heat, DH is negative

If a reaction absorbs heat, DH is positive

In a chemical reaction, solids can be heated to

the point where the molecules holding their

bonds together break apart and form a liquid.

The most common example is solid ice turning

into liquid water. This process is better known

as melting, or heat of fusion, and results in the

molecules within the substance becoming more

chaotic

q = mHf

How much heat is required to melt 4 kg of

ice at 0 ºC? Remember there is no ΔT in a

phase change.

q = mHv

How much heat is required to turn 12 kg of

water at 100 ºC into steam at the same

temperature? Again, there is no ΔT in a

phase change.

Where are the phase changes? How do you recognize them? Which is which?

(s) is the measure of disorder or randomness

of the particles that make up a system

A system tends to go to a more disordered

state or increased entropy

DG is the energy available to do work

DG = DH –TDS

Calculate Gibbs free energy if DH = - 6760J ,

DS = -197J/K , and the temperature is 298K.

If a reaction has a –DG, then the reaction will

be spontaneous ( it will occur without

outside intervention)

ADP + Pi ATP ΔG° = +30 kJ mol–1

C6H12O6 + 2 ADP → 2 CH3CH(OH)COOH ΔG° = –218 kJ mol–1

Calculate DG using DG = DH - TDS. Also, for

each question, tell whether or not the

reaction will be spontaneous.

a) CH3OH(l) + 1½ O2(g) CO2(g) + 2 H2O(g)

H = -638.4 kJ S = 156.9 J / K

b) 2 NO2(g) N2O4(g)

H = - 57.2 kJ S = -175.9 J / K

Collision Theory

Nature of Reactants

Concentration