ThermochemistrySome like it hot...

Forms of Energy

Potential Energy (gravitational, magnetic, chemical)

Kinetic Energy

Work

Light

Heat

HeatHeat is NOT temperature, but the two are related.

Temperature Heat

Average energy Total energy

High temp, low heat Low temp, high heat

Heat Temperature Heat

Measure with thermometer Can't measure directly

Is a property of an object Can only say how much was gained or lost

UnitsMetric: since heat is a type of energy, we can use the

metric units of energy: Joules (J)

Non-metric: the calorie (cal) is a unit specific to heat.

Unit DefinitionsJoules: 1 J = 1 kg*m2/s2

This looks awful, but has a simple meaning:

One joule is the amount of work it takes to move a one kilogram object a distance of one meter, at an acceleration of one meter per second squared.

Unit Definitionscalories:

One calorie is the amount of heat needed to heat one gram of pure water up by one degree.

Note that it doesn't matter whether it's from 20oC to 21oC or from 80oC to 81oC...it's still one calorie.

Formula Time!The symbol for heat is q The units are J or cal.

This is just like the symbol for distance is d, and it can be measured in different units like m, miles, cm...

If the value of q is positive, heat is going into the object (endothermic)

If the value of q is negative, heat is going out of the object (exothermic)

Formula Time!Because energy can't be created or destroyed, then if

the hot thing loses 50 J (q=-50J), the cold thing must gain 50J (q=+50J)

Or, more generallyq

hot + q

cold = 0

WARNING!

This assumes no heat was lost anywhere. We'll have ways of accounting for that later.

Formula Time!Second formula

q = m*c*T

m is the mass (more stuff = more heat)

c is the heat capacity (or specific heat capacity). This is a number that's specific to each substance—some things heat up more easily than others.

T is the change in temperature (Tfinal

– Tinitial

). Bigger temperature changes = more heat.

One More Relevant Fact

Any two (passive) objects in contact with each other will eventually end up at the same temperature.

So two different objects placed together may have different values for T

initial, but will have the same

value for Tfinal

Summary Heat is a form of energy.

Related to temperature, but is not the same thing.

Measured in Joules or calories

Symbol is q. Negative q is exothermic. Positive q is endothermic.

qhot

+ qcold

= 0

q = m*c*T