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Which two observations below can be evidence that a chemical change has occurred? (Choose 2) (1 point)
Production of bubbles (a gas)
melting
vaporization
production of heat
Which of the following was NOT one of the components of Dalton's Atomic Theory? (1 point)
All elements are composed of tiny indivisible particles called atoms.
The atoms of any one element are identical to those of any other element.
Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.
Which of the following is true about subatomic particles? (1 point)
The mass of a neutron is the same as the mass of an electron.
Neutrons have a negative charge and are the heaviest subatomic particle.
Protons are positively charged and are one of the heaviest subatomic particles.
Electrons are neutral and are the lightest subatomic particle.
Answers
Atoms are divisible into sub atomic particles they are electrons,protons and neutrons .
Electrons are negatively charged particles with mass of 9.1×10^-31 kg nd charge is 1.6×10^-19 C .
Protons are positively charged particles which are present inside nucleus with charge same as electron but with positive sign and mass of 1.67×10^-27 kg .
Neutrons are neutral species with no charge and mass equal to 1.67×10^-27kg.
So accordingly statement 3 is correct as protons are positively charged and are heavier than electron.
(i) Production of bubbles and production of heat are evidences that a chemical change has occured.
(ii) The statement "protons are positively charged and are one of the heaviest subatomic particles" is true.
(i) • Production of bubbles - Formation of bubbles in a chemical reaction indicates that a chemical change has taken place as the bubbles cannot be reverted back to the original compounds.
Example :
The reaction between baking soda and vinegar bubbles out CO₂ which is irreversible. So, it is a chemical change.
NaHCO₃ + CH₃COOH → CH₃COONa + CO₂ + H₂O
• Melting - Melting is a physical change as the products can be solidified to get back the reactants.
Example : Ice ⇄ Water
• Vaporization - Vaporization is also a physical change as the vapours can be condensed back to the the liquid droplets.
Example : Water vapour ⇄ Water
• Production of heat - Production of heat in an exothermic reaction is a chemical change as the reaction cannot be reverted to get back the reactants by supplying the amount of heat lost in product formation.
Example :
CaO + H₂O → Ca(OH)₂ + ∆
(ii) • The mass of a neutron is the same as the mass of an electron - False
Correction - The mass of a neutron is heavier than the mass of an electron.
• Neutrons have a negative charge and are the heaviest subatomic particles - False
Neutrons have no charge and are the heaviest subatomic particles.
• Protons are positively charged and are one of the heaviest subatomic particles - True.
• Electrons are neutral and are the lightest subatomic particle - False
Correction - Electrons are negatively charged and are the lightest subatomic particles.