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 elementb- 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
Two flasks have the same volume and temperature, but contain different gases. Flask 1 contains 5.0 g of O2 gas, while Flask 2 contains 5.0 g of H2 gas. Is the pressure in each flask the same, or different, and why?
(8.78) The pressure is not the same, because 5.0 g of O2 does not have the same number of moles of gas as 5.0 g of H2 because the molar masses are different. Under constant volume and temperature, the pressure is directly proportional to the moles of gas.
Potassium chloride has a solubility of 43 g of KCl in 100 g of H2O at 50 C. Determine if each of the following forms a saturated or unsaturated solution at 50 C.
a- adding 25 g of KCl to 100 g of H2O
b- adding 15 g of KCl to 25 g of H2O
c- adding 86 g of KCl to 150 g of H2O
(9.104)
a- unsaturated
b- saturated
c- saturated
Identify the type of reaction for each of the following:
a- a compound breaks apart into its elements
b- copper and bromine form copper(ii) bromide
c- iron(ii) sulfite breaks down into iron(ii) oxide and sulfur dioxide
d- silver ion from AgNO3 forms a solid with bromide ion from KBr
(7.166)
a- decomposition
b- combination
c- decomposition
d- double replacementA 1.3 g sample of rice is burned in a calorimeter to give off 22 kJ of energy. What is the energy content of the rice, in kcal/g?
(1 cal = 4.184 J)
What are the numbers of protons, neutrons, and electrons in the product of the positron decay of boron-8?
(5.59) berylium-8, has 4 protons, 4 electrons, and 4 neutrons
An airplane is pressurized with air to 650 mmHg.
a- If air is 21% oxygen, what is the partial pressure of oxygen in the airplane cabin?
b- If the partial pressure of oxygen falls below 100 mmHg, passengers can become drowsy. If this happens, oxygen masks are deployed. At what total cabin pressure are oxygen masks deployed?
(8.84)
a- 137 mmHg of O2
b- 476 mmHg cabin pressure
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 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
Draw the Lewis structure for ammonia, NH3.
A 2.00 L container is filled with methane (CH4) gas at a pressure of 2500. mmHg and a temperature of 18 C. How many grams of methane are in the container?
(8.91) 4.42 g of methane
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, and identify the type of reaction:
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, decomposition
b- 3 Mg + N2 --> Mg3N2, combination
c- 2 Al + 2 H3PO4 --> 3 H2 + 2 AlPO4, single replacement
d- C3H4 + 4 O2 --> 3CO2 + 2 H2O, combustion
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+
A gas sample has a volume of 4250 mL at 15 C and 745 mmHg. What is the final temperature, in C, of the gas sample if it is moved to a different container with a volume of 2.50 L and a pressure of 1.20 atm? Assume the amount of gas does not change.
(8.103) -66 C
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 mLb- 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
An ice pack containing 275 g of ice at 0.0 C was used to treat a muscle sprain. When the bag was removed, all of the ice had melted and the remaining liquid water was now 24.0 C. How many kilojoules of heat were absorbed by the ice pack?
(specific heat of water is 4.184 J/(g K), and heat of fusion is 334 J/g)
(3.101) 119 kJ
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
a- iron(III) phosphate
b- dichlorine heptoxide
c- calcium phosphate
d- phosphorus trichloride
e- magnesium carbonate
Glucose is metabolized in living systems. How many grams of water can be produced from the reaction of an excess of glucose with 7.50 L of O2 at 1.00 atm and 37 C?
glucose + 6 O2 ---> 6 CO2 + 6 H20
(8.107) 5.30 g of water
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.