RChem Midterm Review MIXED

Which of the following are pure substances?

(check all that apply)

• H₂O_(l)

• CO_(g)

• K_(s) & Ca_(s)

• NaCl_(aq)

Answer explanation

Pure substances have only one type of particle (anything with aq is aqueous, or dissolved in water)

Which sample has the highest average kinetic energy?

• 20.0g of water at 50.0C

• 10.0g of water at 100.0C

• 30.0g of water at 300K

• 40.0g of water at 350K

Answer explanation

Average kinetic energy = temperature, remember to conver C to K (or vice versa)

Which of the following phase changes are endothermic?

(check all that apply)

• Condensation

• Sublimation

• Freezing

• Boiling

Answer explanation

ENdothermic changes require heat to ENter the system (or, in other words the substance needs to get more energy/hotter)

During which line segment(s) is potential energy increasing?

(check all that apply)

• AB

• BC

• CD

• DE

• EF

Answer explanation

If potential energy is changing then kinetic energy must be staying constant (look for the plateaus of the graph)

How much heat is required to increase the temperature of 1.5 grams of water from 25.C to 75.C?

(round your answer to the tenths place and include proper units on your answer)

Answer explanation

You should use q=mC(deltaT) for this. Proper units its joules or J

The gold foil experiment, performed by Ernest Rutherford, discovered that

• the atom has electrons orbiting the nucleus like planets

• the atom was mostly empty space with a small, dense nucleus

• the atom had electrons in it

• atoms are what make up the matter around us

Answer explanation

The Rutherford model of the atom shows a small nucleus with electrons orbiting around it in a large area of empty space. (Rutherford is the most important guy to know!)

What is the mass number of an atom that contains 4 protons, 5 neutrons, and 6 electrons

• 4

• 5

• 9

• 10

• 11

Answer explanation

Mass # = protons + neutrons

Isotopes are

• atoms of the same element with the same mass number

• atoms of different elements with the same mass number

• atoms of different elements with different mass numbers

• atoms of the same element with different mass numbers

Answer explanation

same #p, different #n (ex C-12 and C-14 are isotopes)

The valence electrons are...

(check all that apply)

• The total number of electrons

• The outer most electrons

• The electrons involved in bonding

• The electrons drawn in a Lewis Dot Diagram

• The lowest energy electrons

Answer explanation

Valence electrons are the outside electrons (last number in the electron config) and are involved in bonding and shown in the lewis dot diagram. The have the highest energy of the electrons in an atom because they are the farthest from the nucleus.

Light (and an atom's bright line spectra) get created as a result of

• ground state electrons absorbing energy to jump to an excited state

• ground state electrons emitting energy to jump to an excited state

• excited state electrons emitting energy to drop to ground state

• excited state electrons absorbing energy to drop to ground state

Answer explanation

Ground state is lowest energy and most stable (preferred) for electrons. Electrons absorb energy to get to an excited (unstable) state and must release that excess energy to return to their stable, ground state.