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Thermochemistry & Lab
100

Classify distilled water:

 element, compound, or mixture?

compound

100

Name Na2SO4.

Sodium Sulfate

100

Balance: Mg + O2 → MgO.

2Mg+O2→ 2MgO

100

What is a precipitate?

An insoluble solid formed in a solution reaction.

100

Define molarity and its unit

M = mol solute / L solution

mol/L.

100

A reaction releases heat. Exothermic or endothermic?

Exothermic

ΔH is negative

200

How many protons, neutrons and electrons are in sodium(Na)-23?

11 protons, 12 neutrons, 11 electrons.

200

Write the formula of calcium nitrate.

Ca(NO3)2

200

Classify: 2KClO3 → 2KCl + 3O2.

Decomposition reaction

200

Which is a strong electrolyte and why?

 NaCl(aq) or Glucose(aq)

NaCl

it dissociates into ions.

200

Calculate molarity: 

0.50 mol NaCl in 2.00 L solution

0.250 M

200

What does ΔH = +85 kJ mean?

Endothermic- absorbs 85 kJ at constant pressure

300

A measurement is close to the accepted value but repeated measurements vary widely. Is it accurate or precise?

accurate

300

Name FeCl3 and N2O5.

Iron(III) chloride

Dinitrogen pentoxide

300

How many moles are in 18.0 g H2O?

Approximately 1.00 mol (molar mass 18.02 g/mol).

300

What precipitate forms when AgNO3(aq) and NaCl(aq) mix?

name the compound

AgCl(s)

Silver chloride.

300

Calculate molarity of 4.00 g NaOH in 250.0 mL.

 Molar mass 40.00 g/mol

0.400 M

300

Calculate q for 100 g water heated from 20°C to 30°C. c = 4.184 J/(g·°C).

+4184 J = +4.184 kJ

400

How many protons, neutrons and electrons are in iron-56, Fe3+?

26 protons, 30 neutrons, 23 electrons.

400

Write formulas for ammonium phosphate and aluminum oxide

(NH4)3PO4 and Al2O3

400

Balance and classify 

C3H8 + O2 → CO2 + H2O.

C3H8 + 5O2 → 3CO2 + 4H2O.

Combustion

400

Write net ionic equation for HCl(aq) + NaOH(aq).

H+ (aq) + OH− (aq) → H2O(l).

400

Volume of 2.00 M HCl needed for 250.0 mL of 0.200 M HCl?

25.0 mL using M1V1 = M2V2

400

Reaction releases 500 J heat; 200 J work done ON system. Find ΔU.

 ΔU=q + w = −500 + 200 J=−300 J.  

500

Chlorine has 75% chlorine-35 and 25% chlorine-37. Calculate average atomic mass.

 (0.75 × 35) + (0.25 × 37)= 35.5 u

500

Empirical formula CH2O; molar mass 180 g/mol. 

Find molecular formula.

C6H12O6. 


500

2Mg + O2 → 2MgO

 How many grams MgO from 12.0 g Mg and excess O2?

 (12.0 / 24.31) × 40.31

19.9 g MgO.

500

Write net ionic equation for BaCl2(aq) + Na2SO4(aq).

Ba2+ (aq) + SO4 2− (aq) → BaSO4(s).

500

How many grams NaCl for 500.0 mL of 0.300 M solution? Molar mass 58.44 g/mol.

8.77 g NaCl

500

In peroxide decomposition, concentration changes; time until bubbling stops is measured. Identify variables

Independent: concentration. 

Dependent: time until bubbling stops

600

A compound contains 40.0% C, 6.7% H and 53.3% O by mass. Find its empirical formula.

CH2O. In 100 g: C ≈ 3.33 mol, H ≈ 6.65 mol, O ≈ 3.33 mol; ratio 1:2:1.

600

Name Cu(NO3)2 and PCl5. 

Why do naming systems differ?

Copper(II) nitrate and phosphorus pentachloride.

 Ionic naming uses a Roman numeral; molecular naming uses prefixes.

600

N2 + 3H2 → 2NH3

 Given 2.0 mol N2 and 3.0 mol H2, identify limiting reactant and NH3 formed

H2 is limiting

 2.0 mol NH3 forms.

600

For Zn + CuSO4 → ZnSO4 + Cu,

 identify oxidation, reduction and oxidizing agent.

Zn oxidized to Zn2+; Cu2+ reduced to Cu

 Cu2+ is oxidizing agent.

600

Mix 25.0 mL 0.200 M BaCl2 with 30.0 mL 0.100 M Na2SO4. Grams BaSO4 formed? Molar mass 233.39 g/mol

0.700 g BaSO4.

 Sulfate limits: 0.00300 mol × 233.39 g/mol

600

5.0 g sugar dissolves in 100 mL water at 20, 40, 60°C in 130, 85, 48 s. Identify variables, two controls and trend

Independent: temperature

 dependent: dissolution time.

 Controls: sugar mass, water volume. Higher temperature correlates with shorter time