Energy Matters
Identify each of the following as a chemical or physical change:
a- a plant grows a new leaf
b- chocolate is melted for dessert
c- wood is chopped for the fireplace
d- wood burns in the fireplace
(3.79)
a- chemical
b- physical
c- physical
d- chemical
According to Dalton's Atomic Theory, label each of the following statements as true or false. If the statement is false, correct it to make it true.
a- atoms of an element are identical to atoms of another element
b- every element is made of atoms
c- atoms of different elements combine to form compounds
d- in a chemical reaction, some atoms disappear and new atoms appear
(4.97)
a- false, atoms of an element are identical to other atoms of the same element
b- true
c- true
d- false, in a chemical reaction, atoms are rearranged but are not created or destroyed
What wavelength is higher energy, 400 nm or 725 nm?
E=hc/(lambda), so shorter wavelength is always higher energy! 400 nm is higher energy than 725 nm.
How many moles of HC2H3O2 are in 83.9 mL of a 0.243 M HC2H3O2 solution?
0.0204 mol HC2H3O2
Which element was oxidized and which was reduced in the following reaction:
Cu + Br2 ---> CuBr2
Cu was oxidized (lost electrons) and Br was reduced (gained electrons)
A 50.0 g gold cube (density 19.3 g/mL) and a 50.0 g silver cube (density 10.5 g/mL) are added to a graduated cylinder containing 75.5 mL of water. What is the final volume reading of the cylinder, in mL?
(2.120) 82.9 mL
What are the numbers of protons, neutrons, and electrons in the following atoms:
- boron-8
- antimony-57
- a lithium-5 cation
- boron-8: 5 protons, 5 electrons, 3 neutrons
- antimony-123: 51 protons, 51 electrons, 72 neutrons
- a lithium-5 cation: 3 protons, 2 electrons, 2 neutrons
Scientists have found that both light and electrons exhibit a wave-interference pattern when shot through a double-slit experiment. If you had the right equipment, what would you see if you shot He atoms through a double-slit experiment and why?
Also a wave-interference pattern! All matter has some wave-like and some particle-like properties according to wave-particle duality.
What is the molarity of a solution containing 8.0 g of NaOH in a volume of 400.0 mL of solution?
(9.115) 0.50 M NaOH solution
SURPRISE! This is more of a "tiny stuff" question...
How many grams are in 2.25 moles of each of the following:
a- N2
b- NaBr
c- C6H14
(7.128)
a- 63.0 g N2
b- 232 g NaBr
c- 194 g C6H14
A compound is found to contain 85.6% carbon by mass, and 14.4% hydrogen by mass. Determine the empirical formula of the compound.
CH2
Draw the Lewis structure for ammonia, NH3.
Draw the orbital diagram and electron configuration of the following atoms:
- Al
- K
- O
Draw on board!
- 1s(2)2s(2)2p(6)3s(2)3p(1)
- 1s(2)2s(2)2p(6)3s(2)3p(6)4s(1)
- 1s(2)2s(2)2p(4)
Calculate the mass percent (%m/m) of a solution containing 26 g of K2CO3 and 724 g of H2O.
(9.110) 3.5 %(m/m)
Balance the following chemical equations:
a- Si3N4 --> Si + N2
b- Mg + N2 --> Mg3N2
c- Al + H3PO4 --> H2 + AlPO4
d- C3H4 + O2 --> CO2 + H2O
(7.118)
a- Si3N4 --> 3 Si + 2 N2
b- 3 Mg + N2 --> Mg3N2
c- 2 Al + 2 H3PO4 --> 3 H2 + 2 AlPO4
d- C3H4 + 4 O2 --> 3CO2 + 2 H2O
A hot water pack for a patient contains 725 g of water at 65 C. If the water cools to body temperature of 37 C, how many kJ of heat could be transferred to sore muscles?
(specific heat of water is 4.184 J/(g K))
(3.95) 85 kJ
Give the name for the ionic compound PbO2, and indicate the charge on each ion.
(6.119) lead(IV) oxide, O2- and Pb4+
SURPRISE! This is more of a "reaction time" problem.
How many grams of Na are needed to react fully with 18.4 g of Cl2 gas according to the following reaction:
2 Na + Cl2 --> 2NaCl
11.9 g Na
Calculate the final concentration of each solution when water is added to produce each of the following:
a- 25.0 mL of 8.0 M HCl is diluted to 500 mL
b- 50.0 mL of a 15.0 %(m/v) NH4Cl solution is diluted to 125 mL
c- 4.50 mL of 8.5 M KOH is diluted to 75.0 mL
(9.120)
a- 0.40 M HCl
b- 6.00 %(m/v)
c- 0.51 M KOH
When 50.0 g of iron(iii) oxide reacts with carbon monoxide, 32.8 g of iron is produced. What is the percent yield of iron for the reaction?
Fe2O3 + 3 CO --> 2 Fe + 3 CO2
(7.142) 93.8% yield
You dissolve 3.0 g of CaCl2(s) into a calorimeter containing 150.0 g of H2O at an initial temperature of 22.4 C. The final temperature of the water after mixing is 25.8 C. If you assume the specific heat of the solution is still the same as water (4.184 J/g C), what is the enthalpy of mixing per mole of CaCl2?
79 kJ/mol CaCl2
Classify the following as ionic or covalent/molecular, and give the name of each.
a- FePO4
b- Cl2O7
c- Ca3(PO4)2
d- PCl3
e- MgCO3
(6.156)
a- iron(III) phosphate
b- dichlorine heptoxide
c- calcium phosphate
d- phosphorus trichloride
e- magnesium carbonate
Describe and explain the emission spectrum observed from a Ne gas discharge lamp.
The emission spectrum for Ne would appear as a series of discreet lines at specific wavelengths. Because the energy levels in an atom are quantized (only certain energies allowed), and absorption or emission of light in an atom is caused by transitions between energy levels, then the specific wavelengths correspond to specific energies that are exactly the energy differences between different allowed energy levels for Ne.
An antacid tablet contains 450. mg of Al(OH)3. If you take one tablet of antacid, how many mL of stomach acid (0.20 M HCl) will be neutralized?
3 HCl + Al(OH)3 --> 3 H2O + AlCl3
(9.125) 86.5 mL of stomach acid
Chromium and oxygen combine to form chromium(iii) oxide.
4 Cr + 3 O2 --> 2 Cr2O3
Suppose 26.0 g of Cr react with 8.00 g of O2. Identify the limiting reactant, and calculate how many grams of Cr2O3 can be produced.
(7.157) O2 is limiting reactant, 25.3 g of Cr2O3 can be produced