DF 2

Question 1

give a reason why enthalpy changes would needed to be calculated instead of directly measured

Answer 1

because some reactions like the decomposition of calcium carbonate CaCO3 need extreme conditions like 800 degrees Celsius

Question 2

define specific heat capacity

Answer 2

the amount of energy needed to raise the temperature of 1g of substance by 1 Kelvin

Question 3

state the rule of Hess’ cycle

Answer 3

the enthalpy change for any chemical reaction is independent of the intermediate stages, so as long as the initial and final conditions are the same for each route, it doesn’t affect anything

Question 4

why will enthalpy change always stay the same no matter the route

Answer 4

because of the law of conservation of energy- energy cannot be created or destroyed, so as long as the starting point is the same as the end point, the enthalpy change will always stay the same

Question 5

where is ethanol used and state the formula

Answer 5

-C2H5OH
-present in drinks
-used as an alternative as petrol in cars, burned to release energy
-releases energy when metabolised in the body

Question 6

how would you find out the enthalpy changes of formation of a substance

Answer 6

formation of compounds from their elements in their standard states can be found in data books
some have been calculated directly and some indirectly
can be used to calculate the enthalpy change of reaction

Question 7

when you see this, go through the worked examples in DF2 if you don’t want to fail

Answer 7

okay, i’ll do that NOW