Tutor profile: Amit K.
Subject: Physical Chemistry
How much of H2O is formed when 16.0 g of O2 react with 5.0 g of H2?
The balanced equation for the reaction of O2 with H2 to form H2O is written as... O2 + 2H2 -----> 2H2O Masses for O2 and H2 are given so we need to figure out the limiting reactant here as the mass of the product depends on the limiting reactant. 16.0 g O2 x (1 mol O2/32.0 g O2) = 0.50 mol O2 5.0 g H2 x (1 mol H2/2.0 g H2) = 2.5 mol H2 O2 and H2 react at 1:2 mol ratio, so for 0.50 moles of O2 we need 2 x 0.50 = 1.0 moles of H2. Available moles of H2 are 2.5 and required moles are 1.0. So, hydrogen is excess reactant and O2 is limiting reactant. Now, we would calculate the amount of the product formed. 0.50 mol O2 x (2 mol H2O/1 mol O2) x (18 g H2O/1 mol H2O) = 18 g H2O
Why H2O is liquid and H2S is a gas?
Both the elements O and S belongs to the same group, so their hydrides are same but water is liquid and H2S is gas. The reason is hydrogen bonding. In their group, Oxygen is placed above Sulfur so oxygen is more electron negative than sulfur so oxygen could make a hydrogen bond with hydrogen. Due to the presence of hydrogen bonding, H2O has stronger intermolecular forces as compared to H2S and so it's a liquid as the molecules are closer. In H2S, hydrogen bonding is not present so the molecules are far from each other and so it is a gas.
Subject: Basic Chemistry
A beaker is filled to the brim with ice water. What would happen when the ice melt?
The level of water would drop since ice density is less than water. The relationship between density, volume and mass is density = mass/volume. Since the density of water is more than ice, soon melting the density increases, mass remains same because nothing is going out or in so the volume would decreases as is clear from the formula... volume = mass/density So, the water level would decrease in the beaker.
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