The sides of a metal pan become hot when the pan is placed on a stove burner.
A person gets a sunburn from lying on the beach too long.
An ice cube melts when a person holds it in his hand.
Answer:
An ice cube melts when a person holds it in his hand.
Explanation:
(2) 40. mL at 80.°C (4) 80. mL at 40.°C
O A physical change does not change the chemical formula of the substance
O A physical change has similar characteristics as a chemical change.
A physical change is a change in how the substances react with other substances.
The correct answer is physical change does not change the chemical formula of the substance.
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Answer:
B. a physical change does not change the chemical formula of the substance
Explanation:
Physical change does not change the substance or identity of an object
The reaction is begun with 161.00 g of Si and 139.00 g of Cr2O3.
How many grams of the excess reactant is left after the reaction is complete?
Answer: 122.9 g of will be left from the given masses of both reactants.
Explanation:
To calculate the moles :
According to stoichiometry :
2 moles of require 3 moles of
Thus 0.91 moles of will require= of
Thus is the limiting reagent as it limits the formation of product and is the excess reagent.
Thus (5.75-1.36) = 4.39 moles of excess reagent.
Mass of
Thus 122.9 g of will be left from the given masses of both reactants.
B They both dissociate completely, with little or no reverse reactions.
C They both remain intact when placed in water, with no dissociation taking place.
D They both dissociate completely, with reverse reactions constantly taking place.
2 What happens when the kinetic energy of molecules increases so much that electrons are released by the atoms, creating a swirling gas of positive ions and negative electrons?
A Matter changes to a solid state.
B Matter changes to a liquid state.
C Matter changes to a plasma state.
D Matter changes to a gaseous state.
3 Consider a balloon that has a volume V. It contains n moles of gas, it has an internal pressure of P, and its temperature is T. If the balloon is heated to a temperature of 15.5T while it is placed under a high pressure of 15.5P, how does the volume of the balloon change?
A It doubles.
B It stays the same.
C It increases greatly.
D It decreases slightly.
1) Answer is: B They both dissociate completely, with little or no reverse reactions.
Some of strong acids: HNO₃(nitric acid), HCl(hydrochloric acid), H₂SO₄(sulfuric acid), HI(hydroiodic acid). Strong bases are: sodium hydroxide (NaOH), barium hydroxide (Ba(OH)₂).
For example, hydrochloric acid, completely dissociate in water and give large amount of hydrogen ions (H⁺): HCl(aq) → H⁺(aq) + Cl⁻(aq).
Sodium hydroxide completely dissociate in water:
NaOH(aq) → Na⁺(aq) + OH⁻(aq).
2) Answer is: C Matter changes to a plasma state.
Plasma is a an ionised gas with highly electrical conductivity.
In solid, molecules are closely packed, stiff and do not changes of shape or volume. Solid object (for example iron) does not take on the shape of its container.
Liquids have definite volume, but no fixed shape.
Gases (for example nitrogen and neon) not have definite volume and fixed shape, it depends on its container.
3) Answer is: B It stays the same.
p₁ = P; initial pressure.
p₂ = 15.5 P; final pressure.
V₁ = V: initial volume.
V₂ = ?: final volume.
T₁ = T; initial temperature.
T₂ = 15.5T; final temperature.
The combinated gas law: The volume of a given amount of gas is proportional to the ratio of its Kelvin temperature and its pressure: p₁·V₁/T₁ = p₂·V₂/T₂.
P·V/T = (15.5P · V₂) / 15.5 T.
V₂ = V₁ = V.
Answer:
1). B
2). C
3). B
Explanation:
b. demonstrated how amino acids can form from the environment
c. confirmed that the ultimate source of amino acids and proteins is from plants
d. not yet determined the source of amino acids