According to the topic on stars, galaxies and the universe, the characteristics that are used to classify stars are color, temperature, size, elemental or compound composition, and brightness. Among these factors give, the characteristic not used to classify stars is distance from the earth.
Answer:
B. an air-conditioning system.
Explanation:
Refrigeration is defined as a process of cooling a system to lower temperature below the surrounding temperature while the removed heat is rejected at higher temperatures.
Heat pumps use the heat output of the refrigeration process, which may also be designed to be reversible, but are otherwise similar to air conditioning units.
Answer:
the answer b because
The SI base unit for amount of substance is the mole. 1 mole is equal to 1 moles AgNO3, or 169.8731 grams.
Explanation:
Answer:
Mass = 73.73 g
Explanation:
Given data:
Mass of Mg used = 24.48 g
Mass of HCl used = ?
Mass of hydrogen gas produced = 2.04 g
Mass of Magnesium chloride produced = 96.90 g
Solution:
Chemical equation:
Mg + 2HCl → MgCl₂ + H₂
Number of moles of Mg:
Number of moles = mass/ molar mass
Number of moles = 24.48 g/ 24.305 g/mol
Number of moles = 1.01 mol
Now we will compare the moles of Mg with HCl from balance chemical equation.
Mg : HCl
1 ; 2
1.01 : 2/1× 1.01 = 2.02 mol
Mass of HCl react:
Mass = number of moles × molar mass
Mass = 2.02 × 36.5 g/mol
Mass = 73.73 g
Scientists use carbon-14 to date ancient fossils.
Plants and animals absorb carbon-14 produced by cosmic rays. The ratio of C-14 to C-12 is constant when they are alive.
When they die, the C-14 decays to C-12, and the ratio changes.
Carbon-14 has a half-life of 5730 years. Thus, the object loses half its C-14 every 5730 years.
Scientists can use the C-14 to C-12 ratio to date fossils up to 70 000 years old.
