Answer:
15 h
Explanation:
Okay, the first thing that we all have to know before we can answer this question is that this Topic that is, Chemistry of Radioactivity is related to kinetics in a way that Radioactive disintegration follows the first order of Reaction which is under kinetics. So, we will be using the first order kinetics rate law to answer this question. Using the equation (1) below;
k =[ 2.303/ t ]×log ([N°}/ [Nr]) --------(1).
We are given from the question that N° = initial sample = 0.8 mg and Nr= sample remaining = 0.2 and the time taken = t= 30.0 h.
k= (2.303/ 30.0 h ) × log (0.8/0.2).
k=0.076768 h^-1 × log (4).
k= 0.076768 h^-1 × 0.6021.
k= 0.0462 h^-1.
Therefore, using the formula for Calculating half life below for first order kinetics we will be able to find out answer.
k = ln 2/ t(1/2). Where t(1/2) is the half life.
t(1/2) = ln 2/ k.
t(1/2) = ln 2 / 0.0462 h^-1.
t(1/2)= 0.6931/0.0462 h^-1.
t(1/2)=15 h
Answer:
C. Magnetization of iron
Explanation:
This is a chemical change and cannot be undone by physical means therefore it isn't a physical change
Answer: The number of moles in 250.0 L of He at STP is 11.0 mole.
Explanation:
- It is known that 1.0 mole of a gas at STP conditions will occupy 22.7 L.
- To show this information: STP means that T = 0.0 °C = 273.15 K and P = 1.0 kPa = (100/101.325) = 0.9869 atm.
- From the ideal gas law: PV = nRT.
- Where, P is the pressure in atm <em>(P = 1.0 atm at STP).</em>
- n is the number of moles (n = 1.0 mole).
- R is the general gas constant (R = 0.0821 L.atm/mol.K).
- T is the temperature in K (T = 273.15 K at STP).
- and now we can get the volume of 1.0 mole at STP: V = nRT/P
- V = (1.0 mole x 0.0821 L.atm/mol.K x 273.15 K) / (0.9869 atm) = 22.7 L.
- Now, we can get the number of moles of 250.0 L of He at STP:
<em>Using cross multiplication:</em>
1.0 mole → 22.7 L
??? mole → 250.0 L
- The number of moles in 250.0 L of He at STP = (250.0 L x 1.0 mole) / (22.7 L) = 11.01 mole ≅ 11.0 mole.
Answer:
the solar heat source from the sun is what gives us most of the heat
Explanation: