science 7.3

products and energy

In an exothermic reaction the reactants yield...

true exothermic becomes endothermic if exothermic. goes in opposite direction and endothermic becomes

true or false since exothermic reactions and endothermic reactions have opposite energy changes, if either one proceeds in the opposite direction then it becomes the other.

energy is needed to break bonds in reactants molecules. explain the energy process

energy is then released when bonds are formed in product molecules. by adding up the bond energies in the reactants and products, you can determine whether energy will be released or absorbed

even though energy is released by exothermic reactions, what must be added first to break bonds in the reactants?

energy must first be added

what do breaking bonds require?

energy, and forming bonds releases energy

respiration = the combustion of glucose.

every time your cells need energy they complete

the energy difference between reactants and products is often released as...

heat

fireflys glow in dark because a chemical reaction that emits light is taking place. similarly when you activate a glow stick a chemical reaction that causes the glow stick to emit light occurs.

how is a glow stick like a firefly?

ultraviolet light

in order to make microchips a reaction is used which involves a material called photoresist. whose properties change when exposed to

silicon. the resulting circuits are called microchips or chips

in the 1950's engineers figured out how to replace tubes and wires used in electronic devices with thin layers of material placed on a piece of

chemical reaction in a car engine that remove the unwanted waste products from the combustion of gasoline.

in the 1970's engineers developed a device called a catalytic converter to create

smog or acid rain

in the case of gasoline combustion some of the compounds don't burn completely producing gases that lower the efficiency of

one example of an endothermic reaction of this type

is the decomposition of water by electrolysis. in this case, the energy that is absorbed is in the form of electrical energy

exothermic chemical reactions also occur in living things. some of these reactions release energy as heat, and others release energy as...

light

respiration.

living cells obtain energy from glucose molecules through the process of

waste products

no chemical reaction is ever completely efficient. sometimes a chemical reaction makes unwanted

in this case, the energy that is absorbed is in what form?

of electrical energy - when the electric current is turned off, the reaction stops.

cell phones

one of the many uses of silicon chips is in

unlike many other endothermic reactions, ________________________ doesn't absorb energy as heat?

photosynthesis

the basic food used for energy by almost all living things. for example animals obtain glucose molecules by eating plants or eating other animals.

photosynthesis stores energy from the sun in the form of stored energy like fossil fuels and sugar glucose. the glucose molecules produced by photosynthesis make up

probably the most important series of endothermic reactions on earth is...

photosynthesis.

these types of energy changes can also be observed in different...

physical changes: such as dissolving or changing state

during photosynthesis,

plants absorb energy from sunlight to turn carbon dioxide and water into oxygen and glucose, which is a type of sugar molecule.

endothermic reactions of photosynthesis

plants store energy through

combustion

plants store energy through photosynthesis. cars and trucks release this energy through

energy

respiration is the combustion of glucose to obtain

endothermic reactions. when the energy is needed it is released by exothermic reactions.

the energy in sunlight is stored as

growth of new cells, movement or any life function.

the energy released by respiration can be used for

in exothermic reactions, what produces more energy?

the formation of bonds in the products. overall, more energy is released than is added

silicon which is the second most common element in earths crust after oxygen.

the most common semiconductor material is the element

printing of books and newspapers and a similar reaction occurs in photocopiers and laser printers.

the reaction of photoresist with ultraviolet light is an important chemical reaction. the same type of material is used in the

catalysts

the series of chemical reactions in respiration involves enzymes which are

what is the difference in energy usually absorbed from?

the surroundings as heat (this often causes a decrease in the temperature of the reaction mixture)

^ one example is the reaction of powdered aluminum metal with a type of iron oxide, what is this reaction known as?

the thermite reaction equation for this reaction: 2Al + Fe2O3 (yields) Al2O3 + 2Fe (this reactions released enough heat to melt the iron that's produced. in fact, this reaction is used to weld iron rails together

what happens is more energy is released when the products form than is needed to break the bonds in the reactants?

then energy is released during the reaction.

if more energy is required to break the bonds in the reactants than is released when the products form...

then energy must be added to the reaction. that is, the reaction absorbs energy

the state change from a liquid to a solid, or freezing, released energy-

this is an—- exothermic process

the state change from a solid to a liquid, or melting, absorbs energy

this is an—— endothermic process

catalysts (enzymes) for each step. with the help of enzymes these reactions take place quickly and automatically.

to make these life functions go quickly, the body uses

true or false- in endothermic reactions often produce a decrease in temperature

true

true or false: all endothermic reactions absorb energy. however, they do not all absorb energy as heat

true

true or false- some chemical reactions release excess energy as light instead of heat

true - for example : glow sticks work by a chemical reaction that releases energy as light

true

true o false all common combustion reactions are exothermic

true

true or false other sources of energy used on earth includes energy in fossil fuels such as coal and petroleum as well as energy obtained from food.

true

true or false respiration is the reverse of photosynthesis.

many steps occur in the process of photosynthesis, but the overall chemical reaction is...

6CO2 + 6H2O (yields) C6H12O6 + 6O2

products

In an endothermic Reaction the reactants plus energy yield...

energy

Exothermic and endothermic reactions work together to supply what?

true

True or false an endothermic reaction absorbs energy so energy is on the reactant side of the chemical equation.

True

True or false exothermic reaction releases energy so energy is on the product side of the equation.

what does breaking a bond between carbon and hydrogen require?

a certain amount of energy. this amount of energy is different from the amount of energy needed to break a bond between carbon and oxygen, or between hydrogen and oxygen

what does the release of heat cause?

a change in the temperature of the reaction mixture

exothermic reaction example the state change from a liquid to a solid or freezing.

a chemical reaction in which energy is released to the surroundings as heat

some reactions are highly exothermic, what do these reactions produce?

a great deal of heat and significantly raise the temperature of their surroundings

the sun

a large amount of the energy we use on earth comes from

a semiconductor

a material that can precisely control the conduction of electrical signals

endothermic reaction examples are the state change from a solid to a liquid, or melting,.

a reaction in which energy is absorbed

what do exothermic chemical reactions often produce?

an increase in temperature

in endothermic, are the bond energies of the reactions greater or less than the bond energies of the products

are greater

what is the energy associated with bonds called?

bond energy

what do chemical reactions involve?

breaking binds in reactants and forming new bonds in products

true

true or false the energy stored in plants through photosynthesis can also be released in other ways. energy from fossil fuels such as petroleum, natural gas and coal formed from fossilized materials (mainly plants) that had been under high temperature for millions of years. when these plants were alive they stored energy in the bonds of their molecules and these remain and can be released for example the burning of gasoline in a car releases this energy enabling the cars engine to work.

true or false - in exothermic reactions , the bond energies of the reactants are less than the bond energies of the products...

true- as a result, less energy is needed to break the bonds in the reactants than is released during the formation of the products.

true or false: all common combustion reactions, such as the combustion of methane, are exothermic.

true- to determine how energy changes in this reaction, the bond energies in the reactants-oxygen and methane-and in the products-carbon dioxide and water-can be added and compared