A metal surface becomes dull because of continued abrasion physical change or chemical

The answer is C. The specific amount of energy released when excited electrons fall back to the ground state produces an emission spectrum. That energy is emitted as photons with precise wavelengths corresponding to the energy differences between levels. Because each element yields a characteristic set of wavelengths, the emission spectrum can be used to identify the element in the sample.

Answer: C. 151 g

Solution: The balanced equation given is:

From this equation, the ratio of moles between all substances is 1:1. We have 117 grams of LIOH and 141 grams of HBr available and need to calculate the theoretical yield of LiBr.

We should convert each reactant’s grams into moles to identify the limiting reagent since the theoretical yield relies on it.

Molar mass for LiOH = 6.94 + 15.999 + 1.008 = 23.947 grams per mole

Molar mass for HBr = 1.008 + 79.904 = 80.912 grams per mole

To find the moles of each reactant, we divide their grams by their respective molar masses.

Moles of LiOH = = 4.89 mol

Moles of HBr = = 1.74 mol

As there are fewer moles of HBr, it is the limiting reactant. With a 1:1 mol ratio between HBr and LiBr, 1.74 moles of LiBr can be produced.

Molar mass of LiBr = 6.94 + 79.904 = 86.844 grams per mole

The mass of LiBr formed = = 151 g LiBr

Based on calculations, the theoretical yield of LiBr is 151 g, hence the correct answer is C.

There are 6.022*10^23 molecules in one mole of carbon. To find out how many moles correspond to 7.87*10^7 molecules, we let the number of moles be represented by ‘x’. From this, we establish a ratio: 1 mole corresponds to 6.022*10^23 molecules, while x moles correspond to 7.87*10^7 molecules. Using cross multiplication, we derive x = 7.87*10^7 / 6.022*10^23, leading to the conclusion that x = 1.3*10^-16.

Answer:

4.86×10^23 lead molecules

Explanation:

Using the provided equation, 2 moles of ammonia produces 3 moles of lead.

Thus:

2 mol NH3/ 3 mol Pb

By utilizing this proportion, we can calculate the quantities for each molecule. For 5.38 mol NH3:

(5.38 NH3)(3 Pb/ 2 NH3) = (5.38)(3/2) mol Pb = 8.07 mol Pb

Next, we will apply Avogadro's number to determine the total number of molecules.

(8.07)(6.02×10^23) = 4.86×10^23 lead molecules

Answer:

a. the temperature changes will be identical

Explanation:

Dissolving sodium hydroxide (NaOH) in water is an exothermic process, with the heat released calculated using:

Q = m×C×ΔT

Where Q indicates the heat released, m refers to the mass of the solution, C is the specific heat, and ΔH stands for temperature change.

The specific heat of both solutions remains the same (because both are the same solutions). Specific heat = C.

m denotes the mass of the solutions: 102g for experiment 1 and 204g for experiment 2.

The heat released, Q: If 2g releases X heat, then 4g releases 2X.

Thus, the temperature change for each experiment is:

Experiment 1:

X / 102C = ΔT

Experiment 2:

2X / 204C = ΔT

X / 102C = ΔT

Indicating that,

a. the temperature changes will be identical