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Thermochemistry

Gives off heat (emits)

exothermic

Absorbs heat

endothermic

It flows from hot to cold objects and is known by the letter “q”

heat

The study of energy changes that occur during chemical reactions

thermochemistry

What is a calorie or joule?

Unit of heat (q)

Defined as the amount of heat needed to increase the temperature of an object by 1oC.

Heat capacity

Defined as the amount of heat needed to increase 1 gram of an object by 1oC.

Specific heat or specific heat capacity

The formula for q?

q = C x m x T

Solve the previous equation for the other three variables.

C = q/mTm = q/CTT = q/Cm

A balance bar has 200 Calories. How many kilojoules is this? How

many joules is this?

836.8 kj836,800 joules

True or False. cal/oC is an acceptable unit for specific heat.

False, cal/goC

True or False. Metals generally have a higher specific heat

capacity than water.

False

True or False. Metals generally have a higher specific heat capacity

than molecular compounds.

False

You measure 1200 joules of heat during a 30oC temperature change with a

substance that weighs 100 g. What is the specific heat of the substance.

0.40 J/goC

During a phase change, the temperature of a substance ________.

Remains constant

A calorimeter can effectively measure the heat of another

substance because of the ____________?

Law of Conservation of Energy

H of fusion involves which phase change?

Melting

H of solidification involves which more commonly known phase change?

Freezing

If the percent mass of a solution weighing 300 g is 6%, what is the

mass of the solute?

.06 = x/300gx = 18 g

The heat content of a system at a constant pressure is known as the

________ of that system.

enthalpy

What is the enthalpy change in a chemical reaction known as?

Heat of reaction, H

If the H of a reaction is negative then the reaction is _______ .

exothermic

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

Heat of combustion

The enthalpy change when a mole of solute is dissolved in a solvent.

Heat of solution

True or False. The quantity of heat absorbed when a solid melts is the

same as the quantity released when the substance freezes.

True. Hfus = -Hsolid.

What makes Hess’s law useful?

It allows you to determine heats of reactions indirectly

The change in enthalpy that involves the formation of one mole of a compound from its

elements (at 25oC) is known as?

Standard heat of formation, (Hf

o)

True or False. The standard heat of a reaction can be calculated

by the following equation …Ho = Hf

o(products) - Hf

o(reactants)

True