Calculating Product with a Limiting Reactant
Nitrogen gas reacts with hydrogen gas to form ammonia:
N2+3H2→2NH3
If you start with 2.0 mol N2 and 3.0 mol H2, which reactant is limiting?
Hydrogen (H₂) is the limiting reactant.
If a reaction absorbs heat from the surroundings, is it endothermic or exothermic?
Endothermic
Endothermic = heat goes IN to the system from the surroundings.
Name the compound: NaNO₃
Sodium Nitrate
Draw the Lewis structure of CO₂. What is its molecular shape, electron geometry, and is it polar or nonpolar?
Lewis structure:
O = C = O (each O has 2 lone pairs)
Shape: Linear
Geometry: Linear
Bond angle: 180°
Polarity: Nonpolar
Which atom has the larger atomic radius:
Na or Cl?
Na
If 3.0 mol H2 is limiting, how many moles of ammonia (NH₃) will form?
3H2→2NH3
2.0 mol NH3
In an exothermic reaction, does the temperature of the surroundings increase or decrease?
Increase
Exothermic reactions release heat, warming up the surroundings.
Name the compound: KNO₂
Potassium Nitrite
Draw the Lewis structure of NH₃. What is its molecular shape and polarity?
Shape: Trigonal pyramidal
Geometry: Tetrahedral
Bond angle: ~109°
Polarity: Polar
A gas occupies 2.50 L at 1.00 atm. If pressure increases to 2.50 atm at constant temperature, what is the new volume?
(hint: Boyle's Law)
V2=1.00 L
(1.00)(2.50)=(2.50)(V2)⇒V2=1.00 L
Magnesium reacts with oxygen:
2Mg+O2→2MgO
You have 12.2 g Mg and 10.0 g O₂.
How many grams of MgO can be produced?
Mg: 0.50 mol
O: 0.3125 mol
For 0.50 mol Mg, we require 0.25 mol O₂ → we have 0.3125 mol of O, so Mg is limiting.
Answer: 20.2 g MgO
A cold pack used for injuries becomes colder when activated. What type of reaction is happening?
Endothermic
It absorbs heat from your skin, causing the cooling effect.
Name the compound: FeSO₄
Iron(II) sulfate
Draw the Lewis structure for SO₂ and determine polarity, shape, geometry, and bond angles.
Shape: Bent
Geometry: Trigonal Planar
Bond angle: 120°
Polarity: Polar
The combustion of propane has ΔH=−2220 kJ/mol
Is this reaction exothermic or endothermic, and does the temperature of the surroundings increase or decrease?
Exothermic
The temperature of the surroundings increases
Aluminum reacts with chlorine:
2Al+3Cl2→2AlCl3
You start with 5.0 g Al and 15.0 g Cl₂.
Calculate:
a) Limiting reactant
b) Mass of AlCl₃ produced
c) Mass of excess reactant remaining
a) Cl₂ is limiting
b) 18.8 g AlCl₃
c) 1.19 g Al leftover
When methane gas burns in oxygen and produces a flame, is this an exothermic or endothermic reaction?
Exothermic
Combustion always releases heat and light energy.
Name the compound: (NH₄)₂CO₃
Ammonium carbonate
Draw the Lewis structure for CH₄. Give the electron geometry, molecular shape, and polarity.
Electron geometry: Tetrahedral
Molecular shape: Tetrahedral
Bond angle: 109°
Polarity: Nonpolar
Write the complete electron configuration of Calcium.
Iron(III) oxide reacts with carbon monoxide:
Fe2O3+3CO→2Fe+3CO2
Given 25.0 g Fe₂O₃ and 15.0 g CO:
How many grams of iron (Fe) form?
17.5 g Fe
During an endothermic reaction, what happens to the enthalpy (ΔH) value: positive or negative?
Positive
Energy is absorbed, so the system’s heat content increases → ΔH>0
Name the Compound: Mg(ClO₄)₂
Magnesium perchlorate
Draw the Lewis structure for PCl₃. Identify the molecular geometry, shape, bond angle, and polarity.
Molecular Geometry:
Tetrahedral
Shape: Trigonal Pyramidal
Bond Angle:
~109°
Polarity:
Polar
Which molecule is more polar: HF or HCl?
HF