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1009 available questions

Chemistry · Question 741

Which branch of chemistry studies thermal-energy changes accompanying chemical reactions?

  1. Electrochemistry
  2. Photochemistry
  3. Thermochemistry
  4. Stereochemistry
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Correct answer: C

Thermochemistry

Thermochemistry deals with heat absorbed or released during chemical and physical changes.

Chemistry · Question 742

The minimum extra energy needed for reactants to reach the transition state is called:

  1. Bond energy
  2. Activation energy
  3. Lattice energy
  4. Ionization energy
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Correct answer: B

Activation energy

Activation energy is the energy barrier separating reactants from the transition state.

Chemistry · Question 743

For many reactions near room temperature, a 10 °C temperature rise approximately:

  1. Halves the rate
  2. Doubles the rate
  3. Leaves the rate unchanged
  4. Reduces the rate to one quarter
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Correct answer: B

Doubles the rate

A common empirical rule is that many reaction rates roughly double for a 10 °C rise.

Chemistry · Question 744

Which is a recognized separation technique?

  1. Solvent extraction
  2. Polymerization
  3. Neutralization
  4. Hydrogenation
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Correct answer: A

Solvent extraction

Solvent extraction separates components according to their different solubilities in immiscible phases.

Chemistry · Question 745

In traditional paper chromatography, what acts as the stationary liquid phase?

  1. Water held by cellulose fibres
  2. The developing solvent
  3. Dry nitrogen
  4. The sample spot
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Correct answer: A

Water held by cellulose fibres

Water adsorbed on cellulose fibres functions as the stationary phase in partition paper chromatography.

Chemistry · Question 746

Why does a developing solvent rise through chromatography paper?

  1. Gravity
  2. Capillary action
  3. Centrifugal force
  4. Electrolysis
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Correct answer: B

Capillary action

Adhesion and surface tension draw the solvent through the paper by capillary action.

Chemistry · Question 747

How can a mixture of silver chloride and sodium nitrate be separated?

  1. Add water, stir and filter
  2. Heat strongly and sublime
  3. Use a magnet
  4. Add ethanol and decant
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Correct answer: A

Add water, stir and filter

Sodium nitrate dissolves in water while silver chloride remains insoluble and can be filtered off.

Chemistry · Question 748

Slow cooling of a hot saturated solution generally produces:

  1. Larger crystals
  2. Only amorphous solid
  3. Smaller crystals
  4. No crystals
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Correct answer: A

Larger crystals

Slow cooling allows fewer nuclei more time to grow, producing larger crystals.

Chemistry · Question 749

What is the simplest whole-number ratio of atoms in a compound called?

  1. Molecular formula
  2. Structural formula
  3. Empirical formula
  4. Skeletal formula
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Correct answer: C

Empirical formula

An empirical formula gives the simplest whole-number atom ratio.

Chemistry · Question 750

What is the formula of iron(III) sulfate?

  1. FeSO₄
  2. Fe₂(SO₄)₃
  3. Fe₂SO₄
  4. Fe₃SO₄
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Correct answer: B

Fe₂(SO₄)₃

Two Fe³+ ions balance three sulfate ions, giving Fe₂(SO₄)₃.