Friction is a force that slows the motion between two objects in contact. Derek wants to determine how the surfaces of objects affect the amount of friction. Which of the following will help test this? Slide a wooden block across a table and then across a rug. Compare and contrast the results. Slide a wooden block across a table; slide a metal block across a rug. Compare and contrast the results.

Slide a wooden block across a table; repeat the action at a faster speed. Compare and contrast the results.

Slide a wooden block across a table; repeat the action by turning the block on its side. Compare and contrast the results.

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.

its first and third is your answer i did the qustion the fourth isnt right

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.