Answer:
They have the same number of atoms. = YES
They have different masses. = YES
Explanation:
1 mol of beryllium
• 1 mol of salt
beryllium = Be = Atomic mass: 9.012182
salt = NaCl = Molar mass: 58.44 g/mol
1 mol of water
• 1 mol of hydrogen
water = H2O = Molar mass: 18.01528 g/mol
hydrogen = H = 1g/mole
Which statement is true about these substances?
They have exactly the same mass. = NO
They have different numbers of particles = NO
They have the same number of atoms. = YES
They have different masses. = YES
Avogadro constant means the number of units in one mole of any substance (defined as its molecular weight in grams) is equal to 6.02214076 × 
.
In terms of the most common type of salt, sodium chloride, NaCl is the chemical formula of this salt,
Answer: The pressure of a gas will increase when there is a decrease in the volume of the gas.
Explanation: according to Boyle's law, the volume of a gas will decrease when the pressure is increased at constant temperature and vice versa.
Answer:
The time taken for the cross to become invisible decreases.
Explanation:
We know that one of the factors affecting the rate of reaction is the concentration of reactants. From the collision theory, we know that the higher the concentration of reactants, the greater the possibility of effective collision between reactants leading ultimately to an increase in the rate of reaction. Increase in the rate of reaction implies that the reaction takes a shorter time to reach completion.
In the case of the reaction shown in the question, the point when the reaction is completed is observed by the time take for the cross mark to become invisible. If we look at the given data closely, we will notice that the volume of acid was held constant, the volume of thiosulphate was increased gradually while the volume of water was decreased accordingly. This implies that the concentration of the reactants was increased. Decreasing the volume of water increases reactant concentration.
As explained above, increase in reactant concentration increases the rate of reaction. Hence, the rate of reaction of the acid and thiosulphate increases as reactant concentration increases and the cross mark becomes invisible faster. This implies that in the last column for time taken for the cross to become invisible, the values of time decreases steadily as concentration of reactants increases.
Answer:
1.25 gram of cesium-137 will remain.
Explanation:
Given data:
Half life of cesium-137 = 30 year
Mass of cesium-137 = 5.0 g
Mass remain after 60 years = ?
Solution:
Number of half lives passed = Time elapsed / half life
Number of half lives passed = 60 year / 30 year
Number of half lives passed = 2
At time zero = 5.0 g
At first half life = 5.0 g/2 = 2.5 g
At 2nd half life = 2.5 g/ 2 = 1.25 g
Thus. 1.25 gram of cesium-137 will remain.
