Chem practice paper mc

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Question and 4 answers
Because changing the amount of acid and alkali,the average heat released are similar.
"The mixture rise 6C,one atom is also rise 6C,thus 6C is actually the average temperature increased."
But changing the concentration of acid and alkali,the average heat released of more concentrated solution will be more than that of less concentrated solution,
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So,consider about concentration, but not volume:
Question (1 mol dm^-3)
Ans A (2 mol dm^-3)
Ans B (1 mol dm^-3)
Ans C (0.5 mol dm^-3)
Ans D (0.25 mol dm^-3)
The concentration of ans B is same as that in the question , thus B is the answer.

2012-04-11 20:00:38 補充：
樓上的volume (m) 多左1倍 好似5岩bo
比較下題目同Ans C
題目係 25cm^3 1mol dm^-3
25cm^3 * 1mol dm^-3
=0.025dm^3 *1mol dm^-3
=0.025mol
Ans C係 50cm^3 0.5mol dm^-3
50cm^3 * 0.5mol dm^-3
=0.05dm^3*0.5mol dm^-3
=0.025mol
兩個mole number都一樣mass點會5同。
仲有volume都不等於mass
D=m/V嘛

簡單d既方法:

計左幾多mole水產生先
因為水個mole係直接關係到產生既能量

之後計到 除1除個total volume就ok

例如有1mole 水產生 => 1個unit既energy
有10cm^3 soln in total
你1/10 = 0.1 energy / cm^3

之後有2 mole 水產生 => 2個unit of energy
有10 cm^3 soln in total
你就 2/10 = 0.2 energy / cm^3
比較2個 第2個會吸多d能量。

如果2個value係一樣 就會similar

Temperature rise係會受個mass影響
E=mcΔT
係option C入面
50cm^3 0.5M NaOH + 50cm^3 0.5M HCl
釋放既熱 (E) 同25cm^3 1M NaOH + 25cm^3 1M HCl一樣
( mole of reaction都係一樣)
但volume (m) 多左1倍(+埋之後100cm^3)
所以temp. rise (ΔT) 會細一倍,姐係升3度
B果度
E多左一倍(多左1倍reactants)
m又多左一倍(100cm^3)
所以ΔT不變,姐係升6度

2012-04-11 21:13:33 補充：
用molarity直接比較的確係快而且準
多謝指點

2012-04-11 21:17:26 補充：
兩個mole number都一樣mass點會5同。
仲有volume都不等於mass
D=m/V嘛
p.s.
mole number of NaOH 同 HCl的確一樣,水既mole number係double左,你加熱要加熱埋水架嘛,呢個時侯mass係近似double左(salt既molarity得1M左右唔會影響個mass太大,所以呢個case mass≈volume)

2012-04-11 22:27:56 補充：
我之前都係咁計,係Ka Ho果招直接計molarity都岩,而且冇咁複雜