Consider the intermediate chemical reactions.
ca(s)+ co2(g) + o2(g) → caco(s)
ah, = -812.8kj
ah, = -1,269.8 kj
2ca(s)+ o2(g) → 2cao(s)
the final overall chemical equation is cao(s) + co2(g) → caco3(s). when the enthalpy of this overall chemical equation is
calculated, the enthalpy of the second intermediate equation

is halved and has its sign changed.
is halved.
has its sign changed.
is unchanged.

a pan containing water is placed in a positio n where it is exposed to a 10 mile per hour wind. the pan contains a uniform depth of 1.27 cm of water, is quite wide, and has a length of 2.44 m in the wind direction. the water in the pan is at a constant temperature of 15.5 °c.

substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.