Unit 3 KA4 - chemical energy

Question 1

what is an endothermic reaction?

Answer 1

require heat to be supplied and this is likely to push up costs

Question 2

what is an exothermic reaction?

Answer 2

give out heat and this has to be removed to prevent thermal heating

Question 3

define the meaning of thermal runaway

Answer 3

a situation where an increase in temp changes the conditions in a way that causes a further increase in temp
this causes the reaction to go out of control and can result in an explosion

Question 4

what is stored chemical energy also known as?

Answer 4

enthalpy

Question 5

what is important to remember when writing balanced equations for enthalpies of combustion?

Answer 5

only one mole of the substance being burned is included in the equation

Question 6

what is the enthalpy of combustion?

Answer 6

the energy released to the surroundings when one mole of a substance burns completely in oxygen

Question 7

what is the enthalpy of formation?

Answer 7

the quantity of heat energy taken in or given out when 1 mole of a substance is formed from its elements in their normal state

Question 8

what is hess’s law?

Answer 8

energy can neither be created nor destroyed, but it can be changed from one form to another

Question 9

what does hess’s law state?

Answer 9

the enthalpy change in converting reactants into products is the same regardless of the route by which the reaction takes place
H1=H2+H3=H4+H5+H6

Question 10

what is hess’s law used for?

Answer 10

to calculate enthalpy change, whcih are difficult or impossible to determien, by experiment