7.1-7.3: Energetic of a Reaction and Energy in Reactions

H2

________ and O2 are pumped through two porous electrodeswhere the half- reactions occur.

Fuel cells

________ are affected by low temperatures, becoming less efficient.

fossil fuels

The ________ give out a lot of heat but they cause pollution, with coal the worst culprit, the pollutants in key carbon dioxide which is linked to global warming and other gases that cause acid rain we will look into this later on.

CO2

No ________ or other polluting gases are formed.

Hydrogen

________ has a some unique advantages and disadvantages regarding its use as a fuel:

Nuclear Fuels

________ are not burned.

exothermic reaction

During a(n) ________, more energy is energy is given out when new bonds are made than the energy taken in to break bonds.

Uranium 235

________ undergoes decay and gives off heat energy which nuclear power stations harness, (________ is often used.

fuel

A(n) ________ is a substance which releases energy when burned.

High pressure tanks

________ are needed to store the oxygen and hydrogen in sufficient amounts.

Hand warmers

________ used in the wintertime are based on the release of heat from an exothermic reaction.

silver nitrate

Mixing ________ and sodium chloride solutions gives a white precipitate of silver chloride- and a temperature rise.

Jets of steam

________ are then used to drive turbines for generating electricity.

Endothermic reactions

________ take in energy from their surroundings.

new bonds

More energy is released when ________ are formed than energy required to break the bonds in the reactants.

symbol ΔH

The ________ (delta H) is used to show the change in heat energy.

H

________ is the symbol for enthaply, which is a measure of the total heat of reaction of a chemical reaction.

y axis

The energy of the reactants and products are displayed on the ________ and the reaction pathway (a bit like time) is shown on the x- axis.

chemical reaction

During a(n) ________ there is always an energy change.

Reactants

> Products + energy

This energy is transferred from the chemical energy store of the chemical system to the surroundings and so the energy of the system falls

this means that the energy change is negative

mixing silver nitrate and sodium chloride solutions gives a white precipitate of silver chloride

and a temperature rise

Reactants + Energy

> Products

This energy is transferred to the chemical energy store of the chemical system and so the energy of the system increases

this means the energy change is positive

The neutralization that occurs takes in heat

so your tongue cools

Optional

draw the displayed formula in order to identify the type and number of bonds more easily

Add together all the bond energies for all the bonds in the reactants

this is the ‘energy in

Add together the bond energies for all the bonds in the products

this is the ‘energy out

The fossil fuels

coal petroleum (oil) and natural gas (methane) are the main fuels used around the world