Chem Chapter 5

Front 1

Thermochemistry

Back 1

Studies heat flow in chemical reactions.

Front 2

Energy

Back 2

The capacity to do work, in human terms this would be pep and vitality. If you have a lot of energy you can get a lot of work done.

Front 3

Heat

Back 3

Is a particular form of energy that is transferred from a body at high temperature to a body at low temperature. This is why a cold skillet heats up when you place it on a hot burner on the stove. Scientists used to think heat was a liquid called "caloric," so they used the term "heat flow," to describe the movement of heat from one place to another.

Front 4

System

Back 4

The part of the universe being studied. (The stuff you are examining for heat changes and whatnot)

Front 5

Surroundings

Back 5

The rest of the universe. Practically, the stuff touching the stuff you are looking at. Like if you're cooking, the air surrounding the pan gets hot.

Front 6

State

Back 6

A description of the composition, temperature, and pressure of the system (e.g. the solutions are 50mL each of .5 M NaOH and HCl at 22ºC, and the pressure it 1.0 atm).

Front 7

State Properties

Back 7

properties which depend on the current state of the system, not its past history. Temperature is a state property, it is not dependant on past temperatures. Since temperature is a state property, then

(delta)t = t (final) - t (initial)

Location is also a state property, you were in Washington but are now in Albuquerque. Volume is a state property.

Heat flow is NOT a state property because its magnitude depends on how a process is carried out.

Front 8

q

Back 8

The symbol that defines heat flow.

When q is positive, heat is added to the system.

When q is negative, heat flows out of (is taken away from) the system.

Front 9

Endothermic

Back 9

A reaction in which heat flows from the surroundings into the system (q is positive). Endo, into, heat goes into the system.

Front 10

Exothermic

Back 10

Heat flows out of the system (exo= out of -- as in the exo-skeleton of an insect).

Front 11

Heat flow and temperature eq'n

Back 11

q=C×(delta)t, where

(delta)t=t(final)-t(initial), and C=heat capacity.

Front 12

Heat capacity

Back 12

Is the amount of energy necessary to raise the temperature of the system by 1ºC. Heat capacity units are J/k or J/ºC.

Front 13

Specific heat capacity

Back 13

The amount of heat energy required to raise the temperature of 1g of a substance by 1ºC. This is an intensive property and doesn't depend on the amount of material present.

Front 14

Units of specific heat

Back 14

Joules.

Front 15

C of water

Back 15

4.18J/g׺C

Water has to absorb a lot of energy to raise its temperature.

Front 16

Pure substance of mass eq'n

Back 16

q=m×c×(delta)t

Where q is heat flow (measured in J), m is mass (measured in g), c is specific heat capacity (measured in J/g׺C), and (delta)t=t(final) - t(initial) (measured in ºC)

Front 17

Calorimeter

Back 17

A calorie meter. 1 calorie = 4.184 J, and 1000 of these chemical calories are equivalent to 1 "food calorie". We convert chemical energy into mechanical energy so we can move, electrical energy for our brains, and backup chemical energy, stored fat.

Front 18

Basic qrxn=?

Back 18

-qcal, the only heat flow is between the reaction system and the calorimeter. The heat lost by the reaction is gained by the calorimeter, the numbers must balance perfectly, heat doesn't disappear.

Front 19

Extended qrxn=?

Back 19

qrxn=-Ccal × (delta)t

So we can measure the heat of the reaction if we know the temperature change and the heat capacity of the calorimeter.

Front 20

qrxn=-mwater×C×(delta)t

Back 20

Equation for heat change in chemical neutralization equation.

Front 21

Enthalpy

Back 21

Heat content. For reactions that have the same pressure, use:

(Delta)H=H(products)-H(reactants)

Front 22

Thermochemical equation

Back 22

A balanced chemical equation that includes the enthalpy change for the reaction.

Front 23

Rules for (delta)H

Back 23

1. The sign of (delta)H depends on the direction of the reaction.

2. The magnitude of (delta)H is proportional to the amount of substance, the formation of two moles (instead of just one) of N2H4 would require 2 times as much energy.

Front 24

Hess's Law

Back 24

(Delta)H is a state function, so the path doesn't matter. The enthalpy change for the overall process is equal to the enthalpy changes of the steps.

Front 25

Standard state enthalpy

Back 25

Always 0 for an element in standard state! O2 is 0, H2 is 0, a standalone ion is always at 0 enthalpy.