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1.a student compares the boiling point of substances having different intermolecular forces. which scientific problem is the student most likely investigating?
a) is boiling point affected by the strength of particle attraction?
b) is boiling point correlated to melting point?
c) is boiling point affected by the mass of the sample?
d) is boiling point the temperature at which a substance changes it’s state?

2. the table compares the characteristics of a substance in three different states of matter. which of these best describes the states of the substance represented by state z?
a) it is a solid because strong attractive forces prevent particles from moving
b) it is a liquid because strong attractive forces prevent particles from moving
c) it is a liquid because of weak attractive forces allow for some motion
d) it is a gas because weak
attractive forces allow for some motion

3. which of the following could result from a substance that undergoes a physical change ?
a) it changes irreversibly
b) it undergoes phase change
c) it’s elemental composition is altered
d) it’s atom rearrange to form a new molecule

4. which of the following shows examples of things that converts chemical energy to mechanical energy ?
a) toaster and fan
b) fan and microwave oven
c) airplane and human body
d) microwave oven and blender

5. compare the type of change that occurs when a substance melts and when a substance is set on fire. use complete sentences to justify the type of change that occurs.

6. chemist is designing an experiment to investigate the fact of temperature on the rate of a chemical change . so just a suitable hypothesis for the experiment . also list the dependent independent and controlled variables that can exist in such an investigation .

1) Answer is: A) Is boiling point affected by the strength of particle attraction?

Intermolecular forces are the forces between molecules or particles.  

For example, because of hydrogen bonds, water has higher boiling temperatures than hydrogen sulfide (H₂S).

In molecule of water there are dipole-dipole forces between negatively charged oxygen from one molecule of water and positively charger hydrogen of another molecule of water.  

Hydrogen bond is an electrostatic attraction between two polar groups that occurs when a hydrogen atom (H), covalently bound to a highly electronegative atom such as flourine (F), oxygen (O) and nitrogen (N) atoms.  

2) Answer is: A) it is a solid because strong attractive forces prevent particles from moving.

In solid, molecules are closely packed, stiff and do not changes of shape or volume. Solid object (for example wood) does not take on the shape of its container.

Liquids (for example water) have definite volume, but no fixed shape.

Gases (for example nitrogen and neeon) not have definite volume and fixed shape, it depends on its container.

3) Answer is: B) it undergoes phase change.

A physical change occurs when a substance changes phase.

For example, evaporization is phase change process in which the water changes from a liquid to a gas (water vapor).

Condensation is phase change process in which the water changes from a gas to a liquid.

If the arrangement of particles is changed, that is chemical change or chemical reaction (new substance is formed).

4) Answer is: C) Airplane and human body.

Human body converts food (chemical energy) in, for example, driving bicycle (mechanical energy).

Balanced chemical reaction for cellular respiration (convert chemical energy of glucose):  

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy .

Airplane use combustion of gasoline (chemical energy) for moving turbines.

Balanced chemical reaction of combustion of gasoline (octane):

2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O.

5) Answer is:

a) Melting is a physical change (process), the same substance is present before and after the change, so chemical bonds and melting point of the substance are not changed.

Substance changes phase from solid state to liquid.

b) Combustion (substance set on fire) is chemical change(chemical reaction) with oxygen, so chemical bonds and melting point of the substance are changed.

6) Answer is:

The two main variables in an experiment are the independent and dependent variable.

Dependent variable is the variable being tested and measured in a scientific experiment.

Dependent variables depend on the values of controlled variables.

The dependent variables represent the output or outcome whose variation is being studied.

The dependent variables is chemical change and controlled variable is temperature.

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aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.