According to half life equation:
T(1/2) = ㏑2 / K1
when the T(1/2) = 4 min * 60 = 240 sec
by substitution:
240 = 0.6931 / K1
K1 = 2.9 x 10^-3
when the second T(1/2) = 20 sec, so to get K2:
T(1/2) = 0.6931 / K2
by substitution:
20 = 0.6931 / K2
∴K2 = 3.4 x 10^-2
so, we can get T2 by using this formula:
㏑ (K2/K1) = Ea/R (1/T1 - 1/T2)
by substitution:
㏑(3.4 x 10^-2)/(2.9 x 10^-3) = (24520 / 8.314) (1/298 - 1/T2)
∴ T2 = 396.7 K
= 396.7 - 273 = 123.7 °C
Alterations to the electron-based ionic or covalent bonds between ions or atoms happen during a chemical change. Such changes result in one or more new substances with different physical and chemical properties. This type of change stands in contrast to physical changes which, despite sometimes closely resembling chemical changes, only produce a change in physical properties.
Answer:
Because magnets wear out. Magnetic perpetual machines can never work because magnets eventually wear out. This isn't the reason they don't work. Magnets can lose their magnetism in several ways; Heat them to very high temperatures. Hit them repeatedly with a hammer.
The correct answer is + 32.5 J because heat is absorbed here by copper not evolved also after calculation we will find the H value is positive, lets calculate it:
H = m C Δt where:
m = 10 g
C = 0.13 J/g.°C
Δ t = final temperature - initial temperature = 50 - 25 = + 25 °C
so H = 10 x 0.13 x (+25) = + 32.5 J
