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Question
The phase change H2(g) -> H2(s) is called ________, and the enthalpy change, 
H, for this phase change has a ________ sign.
Answer
This answer is hidden. It contains 22 characters.
Related questions
Q:
In the following picture of an oxide, darkly-shaded spheres represent oxygen atoms or ions and lightly-shaded spheres represent atoms or ions of a third-row element in its highest oxidation state. Tell whether the oxide is covalent or ionic and whether the oxide is acidic or basic. A) covalent and acidic
B) covalent and basic
C) ionic and acidic
D) ionic and basic
Q:
Picture (a) shows p-orbital overlap between carbon and oxygen atoms; picture (b) shows p-orbital overlap between silicon and oxygen atoms. Based on these pictures, it is expected that
A) carbon and oxygen form better σ bonds than silicon and oxygen, so C-O single bonds are stronger than Si-O single bonds.
B) silicon and oxygen form better σ bonds than carbon and oxygen, so Si-O single bonds are stronger than C-O single bonds.
C) carbon and oxygen form better π bonds than silicon and oxygen, so C=O double bonds are stronger than Si=O double bonds.
D) silicon and oxygen form better π bonds than carbon and oxygen, so Si=O double bonds are stronger than C=O double bonds.
Q:
Which element shown on the periodic table above forms an interstitial binary hydride with the formula MXx?
A) element A
B) element B
C) element C
D) element D
Q:
Which element shown on the periodic table above forms a covalent binary hydride with the formula MX4?
A) element A
B) element B
C) element C
D) element D
Q:
What group of elements is most likely to form covalent molecular hydrides?A) AB) BC) CD) D
Q:
The following pictures represent binary hydrides, AHx, where A = Na, Ti, C, or Cl. Lightly-shaded spheres represent H atoms or ions and darkly-colored spheres represent atoms or ions of element A.Which hydride has the lowest melting point?A) hydride (1)B) hydride (2)C) hydride (3)D) hydride (4)
Q:
When 3.600 grams of anhydrous magnesium chloride were exposed to moist air, water was absorbed by the sample. If the resulting hydrated compound has a mass of 4.962 grams, what is the chemical formula of the hydrate?
A) MgCl2 H2O
B) MgCl2 2H2O
C) MgCl2 3H2O
D) MgCl2 4H2O
Q:
Which one of the following compounds is a hydrate?
A) H2O2
B) H2SO4
C) CoCl2 6 H2O
D) Cu(OH)2
Q:
Indicate the coefficient in front of H2O2 when the following redox equation is balanced in an acidic medium.H2O2(aq) + MnO4-(aq) -> O2(g) + Mn2+(aq)A) 2B) 3C) 5D) 7
Q:
In which compound does oxygen have a -1 oxidation state?
A) H2O
B) H2O2
C) O2
D) MgO
Q:
What is the reaction of potassium peroxide in water?A) 2 KO2(s) + H2O(l) -> O2(g) + 2 K+(aq) + HO2-(aq) + OH-(aq)B) K2O2(s) + H2O(l) -> 2 K+(aq) + HO2-(aq) + OH-(aq)C) 2 K2O2(s) + 2 H2O(l) -> 4 K+(aq) + 4 OH-(aq) + O2(g)D) K2O(s) + H2O(l) -> 2 K+(aq) + 2 OH-(aq)
Q:
Which of the following is a peroxide?
A) Li2O
B) K2O2
C) CaO
D) CsO2
Q:
When sodium metal is heated in excess oxygen it tends to form
A) an oxide.
B) a peroxide.
C) a superoxide.
D) an oxide and a superoxide.
Q:
Which of the following oxides has the highest melting point?
A) MgO
B) Na2O
C) D) SO3
Q:
Which will is least likely to form an interstitial hydride?
A) Si
B) Pd
C) Pt
D) Ti
Q:
Which element most readily forms nonstoichiometric hydrides?
A) Pd
B) Na
C) Sb
D) Si
Q:
Which transition metal hydride is commonly used in the purification of hydrogen gas?
A) Cu
B) Fe
C) Pt
D) Pd
Q:
Covalent hydrides of the type MH3 are likely to form with elements of what group?
A) 3A
B) 4A
C) 5A
D) 6A
Q:
The net ionic reaction of solid CaH2 with water isA) CaH2(s) + 2 H2O(l) -> Ca(OH)2(aq) + 2 H2(g)B) CaH2(s) + 2 H2O(l) -> Ca2+(aq) + 2 OH-(aq) + 2 H2(g)C) H-(aq) + H2O(l) -> OH-(aq) + H2(g)D) CaH2(s) + H2O(l) -> CaO(s) + 2 H2(g)
Q:
The dissociation of D2O is shown below.D2O D+(aq) + OD-(aq) K = 1.95 10-15 at 25CIn order to be acidic a D2O solution must have a pH (= pD) that isA) greater than 7.00B) greater than 7.35C) less than 7.00D) less than 7.35
Q:
Which isotope of diatomic hydrogen should have the highest heat of vaporization?
A) H2
B) D2
C) T2
D) The values are equal.
Q:
The strongest homonuclear single bond isA) H-HB) C-CC) N-ND) O-O
Q:
The bright colors of anodized titanium are due toA) electrodeposition of organic dyes on the titanium surface.B) the formation of a titanium alloy with chromium and copper.C) iridescence involving the semitransparent outer layer of TiO2.D) trapping of organic dye molecules in a spongy TiO2 matrix.
Q:
Chromium can be electroplated from an aqueous solution containing sulfuric acid and chromic acid, H2CrO4. What current is required to deposit chromium at a rate of 1.25 g/min?
A) 38.1 A
B) 38.7 A
C) 116 A
D) 232 A
Q:
How many grams of chromium metal are plated out when a constant current of 8.00 A is passed through an aqueous solution containing Cr3+ ions for 40.0 minutes?
A) 3.45 g
B) 6.15 g
C) 10.3 g
D) 31.0 g
Q:
The electrolysis of an aqueous solution of NS produces oxygen at the anode according to the following equation:Calculate the volume of at STP that is produced by the passage of 3.00 A through this solution for 150 minutes.A) 1.57 LB) 0.0261 LC) 6.28 LD) 0.0700 L
Q:
O2(g) + 4 H+(aq) + 4 e--> 2 H2O(l) E = +1.23 VI2(s) + 2 e- -> 2 I-(aq) E = +0.54 V2 H2O(l) + 2 e- -> H2(g) + 2 OH-(aq) E = -0.83 VMg2+(aq) + 2 e- -> Mg(s) E = -2.37 VBased on the data above, electrolysis of an aqueous solution of MgI2, with inert electrodes, is expected to produceA) Mg at the cathode and I2 at the anode.B) H2 at the cathode and I2 at the anode.C) Mg at the cathode and O2 at the anode.D) H2 at the cathode and O2 at the anode.
Q:
A steel pipe can be protected from corrosion by attaching the pipe to a piece of magnesium because
A) magnesium forms a tight oxide coating.
B) magnesium is more easily oxidized than iron.
C) magnesium is inert.
D) magnesium and steel form a corrosion resistant alloy.
Q:
Which of the following statements concerning the rusting of iron is false?
A) The oxidation site can occur at a different place on the metal surface than the reduction site.
B) The metal is reduced.
C) The rusting of iron requires both oxygen and water.
D) Salt increases the rate of corrosion by providing ions to carry the current.
Q:
Shown below are the reactions occurring in the direct methanol fuel cell (DMFC).I 2 CH3OH(aq) + 2 H2O(l) -> 2 CO2(g) +12 H+(aq) +12 e-II 3 O2(g) + 12 H+(aq) + 12 e- -> 6 H2O(l)Overall 2 CH3OH(aq) + 3 O2(g) -> 2 CO2(g) + 4 H2O(l)Which is the anode reaction, and what is being oxidized in the overall reaction?A) I, CH3OHB) I, H2OC) II, O2D) II, H+