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Chemical Bonds and Thermochemistry

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  • Refers to a chemical reaction or physical change in which heat is absorbed. That is, the system gains heat; q is positive.
    endothermic
  • What do sodium ions have in common with chloride ions?
    they are both anions
    they both have the same sized charge
    they both form covalent bonds
    they are both cations
  • The heat released during the combustion of C3H8(g) (propane) to produce CO2(carbon dioxide) gas and water vapour is 2222 kJ/mol of C3H8(g). Which of the following is the correct chemical equation for the reaction?
    C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O (g) ΔH = +2222 kJ
    C3H8(g) + 5O2(g) + 2222 kJ → 4H2O (g) + 3CO2(g)
    3CO2(g) + 4H2O(g) → 5O2(g) + C3H8(g) ΔH = –2222 kJ
    C3H8(g)+ 5O2(g) → 3CO2(g) + 4H2O (g) + 2222 kJ
  • Which combination will give you the enthalpy change for the hydrogenation of ethene to ethane, Δ H3 ?
    − Δ H 2 + Δ H 1 − Δ H 4
  • What is the energy change (in kJ) when the temperature of 20 g of water increases by 10C?
    2 x 283 x 4.18
    (20 x 10 x 4.18)/1000
    (20 x 283 x 4.18)/1000
    20 x 10 x 4.18
  • What is the formula for the compound formed by magnesium cation (Mg+2) and a fluoride anion (F-)
    MgF2
  • What would be the best use of graphite?
    decorative stone for rings
    electrode
    used in drill heads
    lubricant because it is soft and slippery with weak forces
  • What is the formula for the cpm[ound formed when a potassium ion(K+) and a sulfide ion (S-2) unite?
    K2S
  • The Lewis (electron dot) structure of the ethanedioate ion is shown. Outline why all the C–O bond lengths in the ethanedioate ion are the same length
    electrons delocalized «across the O–C–O system» or RESONANCE
  • What is the arrangement of the bonds in diamond as shown in this structure?
    tetrahedral - (4 bonds each 109.5 degrees apart)
  • Which change of state is exothermic?
    H2O(l) → H2O(g)
    NH3(g) → NH3(l)
    Fe(s) → Fe(l)
    CO2(s) → CO2(g)
  • What is the suffix for all binary ionic compounds of representative elements?
    -ide
  • The temperature of a 2.0 g sample of aluminum increases from 25C to 30C. How many joules of heat energy were added? (Specific heat of aluminum = 0.90 J/gK)
    9.0
  • In an exothermic reaction, the temperature of the surroundings increases because the molecules in the surrounding have
    a greater potential energy
    a lower kinetic energy
    a greater kinetic energy
    a lower potential energy
  • What is the name of the compound Ni(NO3)2
    Nickel (II) nitrate
  • What is the sum of the charges in a compound?
    0
  • What is the chemical formula for calcium oxide?
    CaO
  • Consider the following equation for the combustion of hydrogen: H2(g) + 1/2 O2(g) → H2O(g) + 243 kJ In order to produce 1215 kJ of heat, how many grams of H2 must burn?
    8.00 g
    10.0 g
    0.250 g
    12.0 g
  • How many covalent bonds does graphite have?
    3
  • Which of the following is a state function?
    work
    temperature
    force
    heat
  • [HL question] if you are in SL 5 marks automatically. Full marks for answer 1 guess only: Which of the following is a non-spontaneous process?
    Graphite turns into diamond
    Water freezes below 0°C.
    Iron exposed to water and oxygen forms rust
    A gas diffuses into a room until it is equally distributed.
  • Which of the following does NOT have an enthalpy of 0 kJ/mol
    I2(s)
    Co(s)
    S8(s)
    H2O(l)
  • Why do MOLTEN ionic solids conduct electricity?
    When an ionic substance is molten the ionic lattice is broken down allowing the ions to move freely and so conduction occurs.
  • Maitha claims that a single sodium ion and a single oxygen ion do not bond together to form a stable binary ionic compound. Is she correct? You must explain completely
    Maitha is correct. The sum of the charges of the two ions must be zero in order for them to form a stable ionic compound.
  • Give at least 2 (two) ways to refer to this adorable looking allotrope of carbon
    any 2: Bucky ball OR C-60 OR fullterene OR buckminsterfullerene
  • What energy changes occur when chemical bonds are broken?
    It depends on the type of bond
    it depends on the state of matter
    Energy is absorbed when they are broken
    Energy is released when they are broken
  • Unknown element W has 2 valence electrons. Unknown element X has 7 valence electrons. Which formula shows the most likely outcome when elements W and X react?
    WX2
  • Why is CHCl3 more polar than CCl4?
    CCl4 is symmetric and therefore no net dipole; CHCl3 is asymmetric
  • In the formation of the compound of sodium chloride
    a sodium atom donates an electron to a chlorine atom
  • What is the electron and molecular geometry for carbon dioxide. From this data, is it polar?
    Electron: linear. Molecular: linear. - It is symmetric therefor NOT POLAR
  • The average bond enthalpies for O-O and O=O are 146 and 496 kJ/mol respectively. What is the enthalpy change, in kJ, for the reaction below? H-O-O-H(g) → H-O-H(g) + ½O=O(g)
    -102
  • An iron block with a mass of 0.11 kg absorbs 504J of heat energy. What is the temperature rise in K? (C = 0.448 Jg-1K-1)
    9.78E-2
    10.23
    1.02E4
    1.10
  • Best explanation here that graphite is softer than diamond
    every carbon atom has a strong bond to the other
    the carbons have 4 bonds
    graphite is in a tetrahedral arrangement
    layers can slide/move
  • What is the chemical formula for the compound barium bromide?
    BaBr2
  • What is the chemical formula for diamond?
    C(s)
  • Which of the following would you expect to have the highest melting point?
    phosphorous trichloride
    magnesium fluoride
    hydrogen chloride
    dinitrogen oxide
  • Which of the following is the definition of an allotrope?
    The same chemical formula but a different structure
    2 or more different physical forms in which an element exist
    Different numbers of neutrons but same protons
    Different states of a compound
  • What is the formula for the compound sulfur hexachloride?
    SCl6
  • Which combination describes the sulfate(IV) ion, SO32– (also known as sulfite ion)?
    A
    B
    D
    C
  • Which pairs of words correctly completes the statement? Ionic compounds form when____ and _____ react.
    metals ; nonmetals
  • Which molecule is most polar?
    CCl 4
    CHF 3
    CClF 3
    CF 4
  • What is the formula for the compound formed when aluminum ions(Al 3+) and chloride ions (Cl -) unite?
    AlCl3
  • Which series shows the correct order of metallic bond strength from strongest to weakest?
    Rb > K > Na > Mg
    Na > K > Rb > Mg
    Mg > Rb > K > Na
    Mg > Na > K > Rb
  • Which rule must be fulfilled by sharing or transferring electrons to create bonds in order for an element to be stable?
    octet rule
  • A chemical formula includes the symbols of the elements in the compound and subscripts that indicate
    the number of atoms or ions of each type
  • Consider the following reaction: N2 (g) + 3H2 (g) ⇌ 2NH3 (g) Which calculation gives ΔHΘ, in kJ, for the forward reaction?
    y + 3x − 6z
  • Why do ionic solids NOT conduct electricity?
    This is due to the fact that ions are not free to move in a solid as they are arranged in an ionic lattice.
  • What is ΔH for the reaction below in kJ? CS2(g) + 3O2(g) → CO2(g) + 2SO2(g) (ΔHf (kJ/mol): CS2(g) = -110, CO2(g) = -390, SO2(g) = -290)
    -860
  • What is the enthalpy change of combustion of urea, (NH2)2CO, in kJ mol−1? 2(NH2)2CO(s) + 3O2(g) → 2CO2(g) + 2N2(g) + 4H2O(l)
    2 × (−394) + 4 × (−286) −2 × (−333)
    1/2 [2 × (−333) −2 × (−394) −4 × (−286)]
    1/2 [2 × (−394) + 4 × (−286) −2 × (−333)]
    2 × (−333) −2 × (−394) −4 × (−286)
  • For which of the following is the sign of the enthalpy change different from the other three?
    CO2(s) → CO2(g)
    2Cl(g) → Cl2(g)
    Na(g) → Na+(g) + e-
    CaCO3(s) → CaO(s) + CO2(g)
  • What is the molecular geometry of the carbonate ion? What would be the angles?
    trigonal planar; 120 degrees
  • What is the charge on group 1 metals?
    1+
  • What is the name of the compound BaCl2
    barium chloride
  • Covalent compounds are formed when atoms
    share valence electrons
  • Calcium (Ca) is in the second column of the periodic table and is classified as an alkaline earth metal. Which of the following formulas shows the ratio of a compound formed from calcium and iodine(I)?
    CaI2
  • What is the metallic ion in the compound CuCl2?
    Cu2+
  • What is the electron and moelcular geometry of sulfate ion? Is it polar?
    It is tetrahedral for both electron and molecular geometry. Since it is an anion it is polar
  • Which statement is correct about the reaction shown? 2SO2(g) + O2(g) → 2SO3(g) ΔH = -196 kJ
    98 kJ of energy are released for every mole of SO2(g)
    196 kJ of energy are absorbed for every mole of SO2(g)
    196 kJ of energy are released for every mole of SO2(g)
    98 kJ of energy are absorbed for every mole of SO2(g)
  • Covalent bonds take place between
    two nonmetals
  • What will the result be when a reaction between bismuth and fluorine takes place?
    BiF3
  • How many resonance structures are there for sulphite ion? How many lone pairs?
    1 lone pair and 3 resonance structures.
  • What is the overall charge of the compound sodium chloride?
    0
  • a property of a substance that is independent of the amount of the substance present.
    intensive (e.g. mp, bp, density)
  • A chemical system in which neither energy nor matter can flow into or out of a system is described as
    a closed system
    an open system
    a chemical system
    an isolated system
  • What is the electron and moelcular geometry of chlorate ion? Is it polar?
    Electron: tetrahedral. Molecular : Trigonal pyramidal. : It is polar because it is both asymmetric and it is an anion. (draw please w lone pair on chlorinei
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