C3 chemical economics

Question 1

define exothermic reactions

Answer 1

one that gives out energy to the surrondings in the form of heat , there will be a rise in temp in the reaction eg buring fuels

Question 2

define endothermic reactions

Answer 2

one that takes in energy/heat from the surronding. this is shwon by a fall in temp
eg. thermal decomposition, these reactions are less common.

Question 3

EXO=

Answer 3

heat/ hot

Question 4

ENDO=

Answer 4

cold

Question 5

what is needed to break bonds

Answer 5

energy must always be supplied to break bonds and energy is released when bnds are formed

Question 6

what happnes to bonds during a endothermic reaction?

Answer 6

they are broken - heat taken in, thus coldness

Question 7

what happens to bonds during an exothermic reaction

Answer 7

they are formed, thus energy release, thus heat/hot temp

Question 8

what do you use specific heat capacity for?

Answer 8

calculate energy transfered

Question 9

what is the SHC (specific heat capcity) of water

Answer 9

the amount of energy needed to raise the temp of 1gram of water by 1degree is
4.2j/g/c

Question 10

how can you find the mass of fuel burned?

Answer 10

subtract the final mass from the inital mass

Question 11

how can you calculate the amount of energy transfered to the water?

Answer 11

mass of water X SHC of water (4.2) X change in temp

Question 12

how can you calculate the enrgy gven out per gram of fuel?

Answer 12

mass of fuel burned

Question 13

how can you make a test fair?

Answer 13

everthing should be the same (excpet what every your measureing the effect of eg. the amount of enrrgy in fuels)
same apparatus
same amount of water
 same temp to start
repeat the experiment several times

Question 14

what is the rate of reaction, what does it mean/show?

Answer 14

how fast the reactants are chaned into products (its over when one of the reactants is used up)

Question 15

what are the slowest reactions?

Answer 15

rusting fo iron and chemical weathering (acid rain0

Question 16

give an example of a moderatly fast reaction?

Answer 16

metal reacting with dilute acid

Question 17

give an exmaple of a fast reaction

Answer 17

burning or explosions

Question 18

how can you recored the rate of a reaction that releases gas?

Answer 18

measure how quickly the gas is produced

eg. change in mass or volume of gas given off

Question 19

how are reaction rates explained?

Answer 19

collision theory

Question 20

what does the rate of a reaction depend on?

Answer 20

1. the collision frequency of reacting particles( the more collisions the faster the reaction)
2. the energy transfered( parlicles have to collide with enough energy to be sucessful)

Question 21

what des the yeild of a reaction depend on?

Answer 21

tthe amount of product id directionaly proportional to the amount of limiting reactant (the one totaly used up)
once the limiting reactant is used up
the reaction cant continue= no more product

Question 22

what is a limiting reactant?

Answer 22

the one thats been completly used up

Question 23

what does it mean to be excess?

Answer 23

to be left over at the end of the raction

this reatcntant is said to be inexcess

Question 24

what does the rate of a reaction depend on?

Answer 24

temp
concetration
a catalyst
size of particles

Question 25

how can you increase the rate of a reaction?

Answer 25

more particle collisions

Question 26

what odes increasing the temp do to a reation?

Answer 26

the particles have more energy so move faster thusmore collisions

Question 27

how do reactios happen

Answer 27

particles colliding with enough energy to cause a rection

Question 28

what does increasig the concentration or pressure do to a reaction?

Answer 28

they are more particles of the ractant in the same volume which makes more collisions more likely
in a gas the molecules are more crowded so the frequency of collisions increases

Question 29

how does changing the surface area affect a reaction?

Answer 29

increasing a reactants surface reas means the particles aroud it have more area to collide with.

Question 30

how does the addition of a catalyst to a reaction affect it?

Answer 30

it speeds up the reaction without chemically changing r being used up. it gives the reactants an area to stick to whee they can bump off each oter. it reduces the enrgy needed by the partilces to react. the overall number of collisions doesnt increase just the number of sucessful ones.

Question 31

how can you calculate the rae of reaction?

Answer 31

find the reaction rate at say 30 second thn divide by 30 for 1 second

Question 32

where is the realtive atomic mass shown?

Answer 32

on the periodic table it is the bigger number at the top left hand corner

Question 33

what is the relative formaula mass?

Answer 33

the relative atomic masses added together for a compond

eg MgO = 24+16=40

Question 34

what does it mean to conserve mass?

Answer 34

during a chemical reaction noatoms are destroyed and no atoms are created., there shoulde the same number of atoms and type on each side of a reaction equation. no mass is lost or gained

Question 35

what are the three importaint steps in calculating masses in reactions?

Answer 35

write out balanced equation
work out the mr ( relative formula mass)
apply the rule ( divide to get one then mulitply to get all)